diff --git a/python/things/dungeon/acid.py b/python/things/dungeon/acid.py
index f16f16b15..c82145058 100644
--- a/python/things/dungeon/acid.py
+++ b/python/things/dungeon/acid.py
@@ -19,6 +19,7 @@ def acid_init(name, text_long_name, text_short_name, tiles=[], left_tiles=[]):
     my.is_interesting(self, True)
     my.is_loggable(self, True)
     my.is_obs_ai(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.is_tickable(self, True)  # for lifespan
     my.lifespan_dice(self, "1d20+20")
diff --git a/python/things/dungeon/ascend_dungeon.py b/python/things/dungeon/ascend_dungeon.py
index b79da3a0d..94162dafd 100644
--- a/python/things/dungeon/ascend_dungeon.py
+++ b/python/things/dungeon/ascend_dungeon.py
@@ -38,6 +38,7 @@ def tp_init(name, text_long_name, text_short_name):
     my.is_described_when_hovering_over(self, True)
     my.is_interesting(self, True)
     my.is_obs_spawn_monst(self, True)
+    my.is_only_one_per_tile(self, True)
     my.light_color(self, "yellow")
     my.light_dist(self, 3)
     my.normal_placement_rules(self, True)
diff --git a/python/things/dungeon/ascend_sewer.py b/python/things/dungeon/ascend_sewer.py
index bc7fee3e9..1d434e3a7 100644
--- a/python/things/dungeon/ascend_sewer.py
+++ b/python/things/dungeon/ascend_sewer.py
@@ -24,6 +24,7 @@ def tp_init(name, tiles=[], left1_tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_interesting(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_tickable(self, True)
     my.light_color(self, "lime")
     my.light_dist(self, 1)
diff --git a/python/things/dungeon/basalt.py b/python/things/dungeon/basalt.py
index b88c40a6e..3e65accfd 100644
--- a/python/things/dungeon/basalt.py
+++ b/python/things/dungeon/basalt.py
@@ -23,6 +23,7 @@ def basalt_init(name, text_long_name, tiles=[]):
     my.is_interesting(self, True)
     my.is_loggable(self, True)
     my.is_obs_ai(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_tickable(self, True)
     my.text_a_or_an(self, "")
     my.text_description_short(self, "Warm to the touch basalt.")
diff --git a/python/things/dungeon/bridge.py b/python/things/dungeon/bridge.py
index 52a2c3735..fef816c0d 100644
--- a/python/things/dungeon/bridge.py
+++ b/python/things/dungeon/bridge.py
@@ -34,6 +34,7 @@ def tp_init(name, tiles=[], bot3_tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_flat(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.on_death_do(self, "bridge.on_death()")
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "Shaky bridge.")
diff --git a/python/things/dungeon/chasm.py b/python/things/dungeon/chasm.py
index ab9165dab..6f7f5efce 100644
--- a/python/things/dungeon/chasm.py
+++ b/python/things/dungeon/chasm.py
@@ -21,6 +21,7 @@ def chasm_init(name, text_long_name, tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_hazard(self, True)
     my.is_obs_ai(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "a")
     my.text_description_short(self, "%%fg=red$A yawning chasm to the unknown below%%fg=reset$ (double click to jump into).")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/corridor.py b/python/things/dungeon/corridor.py
index bb0617034..1e843c181 100644
--- a/python/things/dungeon/corridor.py
+++ b/python/things/dungeon/corridor.py
@@ -15,6 +15,7 @@ def tp_init(name, tiles=[], bot3_tiles=[]):
     my.is_cursor_can_hover_over(self, True)
     my.is_described_when_hovering_over(self, True)
     my.is_flat(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "The dirty dungeon corridor.")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/deep_water.py b/python/things/dungeon/deep_water.py
index 75e5e5a91..1297b6ca3 100644
--- a/python/things/dungeon/deep_water.py
+++ b/python/things/dungeon/deep_water.py
@@ -28,6 +28,7 @@ def tp_init(name, text_long_name, tiles=[]):
     my.is_hazard(self, True)
     my.is_interesting(self, True)
     my.is_obs_ai(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "A pool of deep dank water, with things in it.")
     my.z_depth(self, my.MAP_DEPTH_LIQUID)
diff --git a/python/things/dungeon/descend_dungeon.py b/python/things/dungeon/descend_dungeon.py
index 8cc93ece0..a075996d0 100644
--- a/python/things/dungeon/descend_dungeon.py
+++ b/python/things/dungeon/descend_dungeon.py
@@ -29,6 +29,7 @@ def tp_init(name, text_long_name, text_short_name):
     my.is_described_when_hovering_over(self, True)
     my.is_interesting(self, True)
     my.is_obs_spawn_monst(self, True)
+    my.is_only_one_per_tile(self, True)
     my.light_color(self, "white")
     my.light_dist(self, 1)
     my.normal_placement_rules(self, True)
diff --git a/python/things/dungeon/descend_sewer.py b/python/things/dungeon/descend_sewer.py
index 69b2550f2..5e9744fca 100644
--- a/python/things/dungeon/descend_sewer.py
+++ b/python/things/dungeon/descend_sewer.py
@@ -24,6 +24,7 @@ def tp_init(name, tiles=[], left1_tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_interesting(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_tickable(self, True)
     my.light_color(self, "lime")
     my.light_dist(self, 1)
diff --git a/python/things/dungeon/dirt.py b/python/things/dungeon/dirt.py
index 3eaa5f4df..1a2188e6b 100644
--- a/python/things/dungeon/dirt.py
+++ b/python/things/dungeon/dirt.py
@@ -23,6 +23,7 @@ def tp_init(name, tiles=[], left1_tiles=[], bot3_tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_dirt(self, True)
     my.is_flat(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "Some exciting dirt")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/dry_grass.py b/python/things/dungeon/dry_grass.py
index 766898048..bcd4f320f 100644
--- a/python/things/dungeon/dry_grass.py
+++ b/python/things/dungeon/dry_grass.py
@@ -33,6 +33,7 @@ def tp_init(name, tiles=[]):
     my.is_dry_grass(self, True)
     my.is_grass(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.nutrition_dice(self, "1d4")
     my.on_hit_and_now_dead_do(self, "dry_grass.on_hit_and_now_dead()")
     my.temperature_max(self, 50)
diff --git a/python/things/dungeon/dry_grass_dead.py b/python/things/dungeon/dry_grass_dead.py
index f9fd49974..a5a0a0a84 100644
--- a/python/things/dungeon/dry_grass_dead.py
+++ b/python/things/dungeon/dry_grass_dead.py
@@ -21,6 +21,7 @@ def tp_init(name, tiles=[]):
     my.is_dry_grass(self, True)
     my.is_grass(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.nutrition_dice(self, "1d2")
     my.temperature_max(self, 50)
     my.temperature_min(self, 0)
diff --git a/python/things/dungeon/dry_grass_trampled.py b/python/things/dungeon/dry_grass_trampled.py
index 0f579e5c0..86a14eee3 100644
--- a/python/things/dungeon/dry_grass_trampled.py
+++ b/python/things/dungeon/dry_grass_trampled.py
@@ -30,6 +30,7 @@ def tp_init(name, tiles=[]):
     my.is_dry_grass_trampled(self, True)
     my.is_grass(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.nutrition_dice(self, "1d3")
     my.on_hit_and_now_dead_do(self, "me.on_hit_and_now_dead()")
     my.temperature_max(self, 50)
diff --git a/python/things/dungeon/fire.py b/python/things/dungeon/fire.py
index 83dfa0d66..230244f44 100644
--- a/python/things/dungeon/fire.py
+++ b/python/things/dungeon/fire.py
@@ -33,6 +33,7 @@ def tp_init(name, text_long_name):
     my.is_interesting(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_tickable(self, True)
     my.lifespan_dice(self, "1d20+20")
     my.light_color(self, "orange")
diff --git a/python/things/dungeon/floor.py b/python/things/dungeon/floor.py
index edc3aa3c1..9b250e386 100644
--- a/python/things/dungeon/floor.py
+++ b/python/things/dungeon/floor.py
@@ -22,6 +22,7 @@ def tp_init(name, tiles=[], bot3_tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_flat(self, True)
     my.is_floor(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "The unwashed dungeon floor.")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/floor_green_blood.py b/python/things/dungeon/floor_green_blood.py
index c09aeadba..e58175e32 100644
--- a/python/things/dungeon/floor_green_blood.py
+++ b/python/things/dungeon/floor_green_blood.py
@@ -21,6 +21,7 @@ def tp_init(name, text_long_name):
     my.is_flat(self, True)
     my.is_green_blood(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.normal_placement_rules(self, True)
     my.nutrition_dice(self, "1d4")
diff --git a/python/things/dungeon/floor_ice.py b/python/things/dungeon/floor_ice.py
index fd75b26a1..cdb7982eb 100644
--- a/python/things/dungeon/floor_ice.py
+++ b/python/things/dungeon/floor_ice.py
@@ -22,6 +22,7 @@ def tp_init(name, tiles=[], bot3_tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_flat(self, True)
     my.is_floor(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "The icy dungeon floor.")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/floor_lava.py b/python/things/dungeon/floor_lava.py
index 99ba793a3..7590b4eea 100644
--- a/python/things/dungeon/floor_lava.py
+++ b/python/things/dungeon/floor_lava.py
@@ -22,6 +22,7 @@ def tp_init(name, tiles=[], bot3_tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_flat(self, True)
     my.is_floor(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "The scalding dungeon floor.")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/floor_red_blood.py b/python/things/dungeon/floor_red_blood.py
index 137e38503..3f89d0d69 100644
--- a/python/things/dungeon/floor_red_blood.py
+++ b/python/things/dungeon/floor_red_blood.py
@@ -20,6 +20,7 @@ def tp_init(name, text_long_name):
     my.is_described_when_hovering_over(self, True)
     my.is_flat(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_red_blood(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.normal_placement_rules(self, True)
diff --git a/python/things/dungeon/foliage.py b/python/things/dungeon/foliage.py
index 06667c264..908535d28 100644
--- a/python/things/dungeon/foliage.py
+++ b/python/things/dungeon/foliage.py
@@ -35,6 +35,7 @@ def tp_init(name, tiles=[]):
     my.is_hittable(self, True)
     my.is_interesting(self, True)
     my.is_light_blocker_for_monst(self, True)  # to give cover to the player
+    my.is_only_one_per_tile(self, True)
     my.noise_blocker(self, True)
     my.nutrition_dice(self, "1d6")
     my.temperature_max(self, 50)
diff --git a/python/things/dungeon/foliage_large.py b/python/things/dungeon/foliage_large.py
index 812aab026..3f6155bb8 100644
--- a/python/things/dungeon/foliage_large.py
+++ b/python/things/dungeon/foliage_large.py
@@ -36,6 +36,7 @@ def tp_init(name, tiles=[]):
     my.is_hittable(self, True)
     my.is_interesting(self, True)
     my.is_light_blocker_for_monst(self, True)  # to give cover to the player
+    my.is_only_one_per_tile(self, True)
     my.noise_blocker(self, True)
     my.nutrition_dice(self, "1d8")
     my.temperature_max(self, 50)
diff --git a/python/things/dungeon/foliage_large_sickly.py b/python/things/dungeon/foliage_large_sickly.py
index 1b8306c3b..0ab99978e 100644
--- a/python/things/dungeon/foliage_large_sickly.py
+++ b/python/things/dungeon/foliage_large_sickly.py
@@ -37,6 +37,7 @@ def tp_init(name, tiles=[]):
     my.is_hittable(self, True)
     my.is_interesting(self, True)
     my.is_light_blocker_for_monst(self, True)  # to give cover to the player
+    my.is_only_one_per_tile(self, True)
     my.noise_blocker(self, True)
     my.nutrition_dice(self, "1d5")
     my.temperature_max(self, 50)
diff --git a/python/things/dungeon/foliage_sickly.py b/python/things/dungeon/foliage_sickly.py
index eb9ca5fc6..789156fd2 100644
--- a/python/things/dungeon/foliage_sickly.py
+++ b/python/things/dungeon/foliage_sickly.py
@@ -36,6 +36,7 @@ def tp_init(name, tiles=[]):
     my.is_hittable(self, True)
     my.is_interesting(self, True)
     my.is_light_blocker_for_monst(self, True)  # to give cover to the player
+    my.is_only_one_per_tile(self, True)
     my.noise_blocker(self, True)
     my.nutrition_dice(self, "1d3")
     my.temperature_max(self, 50)
diff --git a/python/things/dungeon/gargoyle_podium.py b/python/things/dungeon/gargoyle_podium.py
index 00814528f..fb2ab4e32 100644
--- a/python/things/dungeon/gargoyle_podium.py
+++ b/python/things/dungeon/gargoyle_podium.py
@@ -14,6 +14,7 @@ def tp_init(name, text_long_name, tiles=[]):
     my.gfx_pixelart_show_outlined(self, True)
     my.gfx_pixelart_submergible(self, True)
     my.is_able_to_fall(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "an")
     my.text_description_short(self, "An empty podium. With claw marks.")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/lava.py b/python/things/dungeon/lava.py
index a1ab8dca9..e1ce09763 100644
--- a/python/things/dungeon/lava.py
+++ b/python/things/dungeon/lava.py
@@ -39,6 +39,7 @@ def lava_init(name, text_long_name, tiles=[]):
     my.is_interesting(self, True)
     my.is_lava(self, True)
     my.is_obs_ai(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_tickable(self, True)
     my.light_color(self, "red")
     my.light_dist(self, 2)
diff --git a/python/things/dungeon/pillar.py b/python/things/dungeon/pillar.py
index eb91583cb..14dbee7eb 100644
--- a/python/things/dungeon/pillar.py
+++ b/python/things/dungeon/pillar.py
@@ -28,6 +28,7 @@ def tp_init(name, text_long_name, tiles=[]):
     my.is_obs_spawn(self, True)
     my.is_obs_throwing(self, True)
     my.is_obs_wall_or_door(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_pillar(self, True)
     my.text_a_or_an(self, "a")
     my.text_description_short(self, "An aged and moss-covered stone pillar.")
diff --git a/python/things/dungeon/portal.py b/python/things/dungeon/portal.py
index b254272c8..c58ae2d3f 100644
--- a/python/things/dungeon/portal.py
+++ b/python/things/dungeon/portal.py
@@ -32,6 +32,7 @@ def tp_init(name, text_long_name, text_short_name):
     my.is_obs_shooting(self, True)
     my.is_obs_spawn_monst(self, True)
     my.is_obs_throwing(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_portal(self, True)
     my.light_color(self, "purple")
     my.light_dist(self, 3)
diff --git a/python/things/dungeon/ripple_large.py b/python/things/dungeon/ripple_large.py
index 124e7ec08..2a5c50870 100644
--- a/python/things/dungeon/ripple_large.py
+++ b/python/things/dungeon/ripple_large.py
@@ -9,6 +9,7 @@ def tp_init(name):
     my.gfx_pixelart_animated(self, True)
     my.gfx_pixelart_reflection(self, True)
     my.gfx_pixelart_shadow(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.is_ripple(self, True)
     my.is_tmp_thing(self, True)
diff --git a/python/things/dungeon/ripple_small.py b/python/things/dungeon/ripple_small.py
index 4f34e5000..330ba9e22 100644
--- a/python/things/dungeon/ripple_small.py
+++ b/python/things/dungeon/ripple_small.py
@@ -9,6 +9,7 @@ def tp_init(name):
     my.gfx_pixelart_animated(self, True)
     my.gfx_pixelart_reflection(self, True)
     my.gfx_pixelart_shadow(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.is_ripple(self, True)
     my.is_tmp_thing(self, True)
diff --git a/python/things/dungeon/rock.py b/python/things/dungeon/rock.py
index 099b23749..6a98ecdf7 100644
--- a/python/things/dungeon/rock.py
+++ b/python/things/dungeon/rock.py
@@ -57,6 +57,7 @@ def tp_init(
     my.is_obs_spawn(self, True)
     my.is_obs_throwing(self, True)
     my.is_obs_wall_or_door(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_rock(self, True)
     my.is_stone(self, True)
     my.is_very_hard(self, True)
diff --git a/python/things/dungeon/rock_ice.py b/python/things/dungeon/rock_ice.py
index b2b8880f7..356c7c720 100644
--- a/python/things/dungeon/rock_ice.py
+++ b/python/things/dungeon/rock_ice.py
@@ -55,6 +55,7 @@ def tp_init(
     my.is_obs_spawn(self, True)
     my.is_obs_throwing(self, True)
     my.is_obs_wall_or_door(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_rock_ice(self, True)
     my.is_very_hard(self, True)
     my.is_wall(self, True)
diff --git a/python/things/dungeon/rock_lava.py b/python/things/dungeon/rock_lava.py
index a51976953..157e39201 100644
--- a/python/things/dungeon/rock_lava.py
+++ b/python/things/dungeon/rock_lava.py
@@ -55,6 +55,7 @@ def tp_init(
     my.is_obs_spawn(self, True)
     my.is_obs_throwing(self, True)
     my.is_obs_wall_or_door(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_rock(self, True)
     my.is_stone(self, True)
     my.is_very_hard(self, True)
diff --git a/python/things/dungeon/small_fire.py b/python/things/dungeon/small_fire.py
index ea5f2623f..0531d9542 100644
--- a/python/things/dungeon/small_fire.py
+++ b/python/things/dungeon/small_fire.py
@@ -30,6 +30,7 @@ def tp_init(name, text_long_name):
     my.is_interesting(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_tickable(self, True)
     my.lifespan_dice(self, "1d10+10")
     my.light_color(self, "orange")
diff --git a/python/things/dungeon/smoke.py b/python/things/dungeon/smoke.py
index 203e18a6c..d75e6b13a 100644
--- a/python/things/dungeon/smoke.py
+++ b/python/things/dungeon/smoke.py
@@ -16,6 +16,7 @@ def tp_init(name):
     my.gfx_pixelart_shadow(self, True)
     my.gfx_pixelart_shadow_short(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.is_smoke(self, True)
     my.is_tickable(self, True)
diff --git a/python/things/dungeon/spiderweb.py b/python/things/dungeon/spiderweb.py
index 881754376..f7d818c06 100644
--- a/python/things/dungeon/spiderweb.py
+++ b/python/things/dungeon/spiderweb.py
@@ -32,6 +32,7 @@ def tp_init(name, tiles=[]):
     my.is_immune_to_cold(self, True)
     my.is_interesting(self, True)  # So robot can see and break out
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_spiderweb(self, True)
     my.is_sticky(self, True)
     my.normal_placement_rules(self, True)
diff --git a/python/things/dungeon/steam.py b/python/things/dungeon/steam.py
index 863504c39..d09e3a7db 100644
--- a/python/things/dungeon/steam.py
+++ b/python/things/dungeon/steam.py
@@ -18,6 +18,7 @@ def tp_init(name):
     my.is_described_when_hovering_over(self, True)
     my.is_interesting(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.is_steam(self, True)
     my.is_tickable(self, True)
diff --git a/python/things/dungeon/wall_dungeon.py b/python/things/dungeon/wall_dungeon.py
index 250256f5c..46dd35dab 100644
--- a/python/things/dungeon/wall_dungeon.py
+++ b/python/things/dungeon/wall_dungeon.py
@@ -57,6 +57,7 @@ def tp_init(
     my.is_obs_spawn(self, True)
     my.is_obs_throwing(self, True)
     my.is_obs_wall_or_door(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_stone(self, True)
     my.is_wall_dungeon(self, True)
     my.is_wall(self, True)
diff --git a/python/things/dungeon/wall_floor.py b/python/things/dungeon/wall_floor.py
index 0bea37254..e7ea34046 100644
--- a/python/things/dungeon/wall_floor.py
+++ b/python/things/dungeon/wall_floor.py
@@ -12,6 +12,7 @@ def tp_init(name, tiles=[], left1_tiles=[], bot3_tiles=[]):
     my.gfx_pixelart_shown_in_bg(self, True)
     my.is_cursor_can_hover_over(self, True)
     my.is_floor(self, True)
+    my.is_only_one_per_tile(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "The unwashed dungeon foundation.")
     my.tick_prio(self, my.MAP_TICK_PRIO_NORMAL)
diff --git a/python/things/dungeon/wall_sewer.py b/python/things/dungeon/wall_sewer.py
index 23cbe8b5d..349a9658b 100644
--- a/python/things/dungeon/wall_sewer.py
+++ b/python/things/dungeon/wall_sewer.py
@@ -52,6 +52,7 @@ def tp_init(
     my.is_obs_spawn(self, True)
     my.is_obs_throwing(self, True)
     my.is_obs_wall_or_door(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_sewer_wall(self, True)
     my.is_stone(self, True)
     my.is_wall(self, True)
diff --git a/python/things/dungeon/water.py b/python/things/dungeon/water.py
index 5da08132d..9b25d1a10 100644
--- a/python/things/dungeon/water.py
+++ b/python/things/dungeon/water.py
@@ -27,6 +27,7 @@ def tp_init(name, text_long_name, tiles=[]):
     my.is_hazard(self, True)
     my.is_interesting(self, True)
     my.is_obs_ai(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_shallow_water(self, True)
     my.text_a_or_an(self, "the")
     my.text_description_short(self, "Some shallow water.")
diff --git a/python/things/dungeon/webball.py b/python/things/dungeon/webball.py
index 3f0fb2787..1a6607184 100644
--- a/python/things/dungeon/webball.py
+++ b/python/things/dungeon/webball.py
@@ -26,6 +26,7 @@ def tp_init(name, tiles=[]):
     my.is_hittable(self, True)
     my.is_interesting(self, True)  # So robot can see and break out
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_spiderweb(self, True)
     my.is_sticky(self, True)
     my.normal_placement_rules(self, False)
diff --git a/python/things/dungeon/wet_grass.py b/python/things/dungeon/wet_grass.py
index a4ef4aa69..2b698c425 100644
--- a/python/things/dungeon/wet_grass.py
+++ b/python/things/dungeon/wet_grass.py
@@ -24,6 +24,7 @@ def tp_init(name, tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_grass(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_wet_grass(self, True)
     my.nutrition_dice(self, "1d5")
     my.temperature_max(self, 50)
diff --git a/python/things/dungeon/wet_grass_trampled.py b/python/things/dungeon/wet_grass_trampled.py
index a5f8e6642..cdad7c446 100644
--- a/python/things/dungeon/wet_grass_trampled.py
+++ b/python/things/dungeon/wet_grass_trampled.py
@@ -21,6 +21,7 @@ def tp_init(name, tiles=[]):
     my.is_described_when_hovering_over(self, True)
     my.is_grass(self, True)
     my.is_interesting(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_wet_grass(self, True)
     my.is_wet_grass_trampled(self, True)
     my.nutrition_dice(self, "1d4")
diff --git a/python/things/effects/attack_green.py b/python/things/effects/attack_green.py
index 4292a2f56..d95a04c7a 100644
--- a/python/things/effects/attack_green.py
+++ b/python/things/effects/attack_green.py
@@ -15,6 +15,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.text_a_or_an(self, "a")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/attack_major_green.py b/python/things/effects/attack_major_green.py
index 9f46456b4..b84a9e99f 100644
--- a/python/things/effects/attack_major_green.py
+++ b/python/things/effects/attack_major_green.py
@@ -15,6 +15,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.text_a_or_an(self, "a")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/attack_major_orange.py b/python/things/effects/attack_major_orange.py
index 1c29e281a..db477d858 100644
--- a/python/things/effects/attack_major_orange.py
+++ b/python/things/effects/attack_major_orange.py
@@ -15,6 +15,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.text_a_or_an(self, "a")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/attack_major_red.py b/python/things/effects/attack_major_red.py
index 54d47e494..1e5834577 100644
--- a/python/things/effects/attack_major_red.py
+++ b/python/things/effects/attack_major_red.py
@@ -15,6 +15,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.text_a_or_an(self, "a")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/attack_orange.py b/python/things/effects/attack_orange.py
index 422be47fc..def12e8bd 100644
--- a/python/things/effects/attack_orange.py
+++ b/python/things/effects/attack_orange.py
@@ -15,6 +15,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.text_a_or_an(self, "a")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/attack_punch.py b/python/things/effects/attack_punch.py
index 3d0887281..5342dcbb6 100644
--- a/python/things/effects/attack_punch.py
+++ b/python/things/effects/attack_punch.py
@@ -17,6 +17,7 @@ def init1(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.text_a_or_an(self, "a")
     my.text_description_short(self, "Punch out.")
diff --git a/python/things/effects/attack_red.py b/python/things/effects/attack_red.py
index fae840159..9cad5c749 100644
--- a/python/things/effects/attack_red.py
+++ b/python/things/effects/attack_red.py
@@ -15,6 +15,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_loggable(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.text_a_or_an(self, "a")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/explosion_cold.py b/python/things/effects/explosion_cold.py
index 7af5e252e..347221467 100644
--- a/python/things/effects/explosion_cold.py
+++ b/python/things/effects/explosion_cold.py
@@ -18,6 +18,7 @@ def tp_init(name, text_long_name, text_short_name):
     my.is_explosion(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.noise_on_born(self, 70)
     my.on_born_do(self, "me.on_born()")
     my.text_hits(self, "blasts")
diff --git a/python/things/effects/explosion_destroy_floor.py b/python/things/effects/explosion_destroy_floor.py
index 963c8953c..4636d62bf 100644
--- a/python/things/effects/explosion_destroy_floor.py
+++ b/python/things/effects/explosion_destroy_floor.py
@@ -22,6 +22,7 @@ def tp_init(name, text_long_name, text_short_name):
     my.is_explosion(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.noise_on_born(self, 100)
     my.on_born_do(self, "me.on_born()")
     my.text_hits(self, "blasts")
diff --git a/python/things/effects/explosion_fire.py b/python/things/effects/explosion_fire.py
index 31e1699d7..b2fa1af52 100644
--- a/python/things/effects/explosion_fire.py
+++ b/python/things/effects/explosion_fire.py
@@ -18,6 +18,7 @@ def tp_init(name, text_long_name, text_short_name):
     my.is_explosion(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.noise_on_born(self, 70)
     my.on_born_do(self, "me.on_born()")
     my.text_hits(self, "blasts")
diff --git a/python/things/effects/explosion_major.py b/python/things/effects/explosion_major.py
index a3fe40b73..baef67fd9 100644
--- a/python/things/effects/explosion_major.py
+++ b/python/things/effects/explosion_major.py
@@ -43,6 +43,7 @@ def tp_init(name, text_long_name, text_short_name):
     my.is_fire(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.light_color(self, "yellow")
     my.light_dist(self, 4)
     my.noise_on_born(self, 100)
diff --git a/python/things/effects/ghost_explosion.py b/python/things/effects/ghost_explosion.py
index a9d532b46..fa14e03bf 100644
--- a/python/things/effects/ghost_explosion.py
+++ b/python/things/effects/ghost_explosion.py
@@ -15,6 +15,7 @@ def tp_init(name):
     my.is_explosion(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.noise_on_born(self, 21)
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
     my.z_depth(self, my.MAP_DEPTH_OBJ)
diff --git a/python/things/effects/green_splatter.py b/python/things/effects/green_splatter.py
index 323409c84..3f8d0085e 100644
--- a/python/things/effects/green_splatter.py
+++ b/python/things/effects/green_splatter.py
@@ -15,6 +15,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_green_splatter(self, True)
     my.is_moveable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.is_splatter(self, True)
     my.is_tmp_thing(self, True)
diff --git a/python/things/effects/magical_effect.py b/python/things/effects/magical_effect.py
index bd27942ca..ec03f33a4 100644
--- a/python/things/effects/magical_effect.py
+++ b/python/things/effects/magical_effect.py
@@ -19,6 +19,7 @@ def tp_init(name):
     my.is_explosion(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.noise_on_born(self, 50)
     my.on_born_do(self, "me.on_born()")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/mob_explosion.py b/python/things/effects/mob_explosion.py
index 7b2ca1c22..5adefb9cd 100644
--- a/python/things/effects/mob_explosion.py
+++ b/python/things/effects/mob_explosion.py
@@ -18,6 +18,7 @@ def tp_init(name):
     my.is_explosion(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.noise_on_born(self, 50)
     my.on_born_do(self, "me.on_born()")
     my.tick_prio(self, my.MAP_TICK_PRIO_VERY_HIGH)
diff --git a/python/things/effects/red_splatter.py b/python/things/effects/red_splatter.py
index deabd7db4..d98ddf247 100644
--- a/python/things/effects/red_splatter.py
+++ b/python/things/effects/red_splatter.py
@@ -13,6 +13,7 @@ def tp_init(name, text_long_name):
     my.gfx_pixelart_show_outlined(self, True)
     my.is_able_to_fall(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.is_red_splatter(self, True)
     my.is_removable_if_out_of_slots(self, True)
     my.is_splatter(self, True)
diff --git a/python/things/effects/teleport_in.py b/python/things/effects/teleport_in.py
index d05a5aa85..a3cbf2eff 100644
--- a/python/things/effects/teleport_in.py
+++ b/python/things/effects/teleport_in.py
@@ -19,6 +19,7 @@ def tp_init(name):
     my.gfx_pixelart_shadow_short(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.light_color(self, "cyan")
     my.light_dist(self, 2)
     my.noise_on_born(self, 100)
diff --git a/python/things/effects/teleport_out.py b/python/things/effects/teleport_out.py
index 12bf929f1..82cf8cd43 100644
--- a/python/things/effects/teleport_out.py
+++ b/python/things/effects/teleport_out.py
@@ -19,6 +19,7 @@ def tp_init(name):
     my.gfx_pixelart_shadow_short(self, True)
     my.is_floating(self, True)
     my.is_loggable(self, True)
+    my.is_only_one_per_tile(self, True)
     my.light_color(self, "cyan")
     my.light_dist(self, 2)
     my.noise_on_born(self, 100)
diff --git a/src/level_biome_chasms.cpp b/src/level_biome_chasms.cpp
index a46c95a76..efbe72ad5 100644
--- a/src/level_biome_chasms.cpp
+++ b/src/level_biome_chasms.cpp
@@ -444,7 +444,11 @@ void Level::create_biome_chasms_place_floors(Dungeonp d, std::string what, int f
           cnt++;
         }
 
-        auto t    = thing_new(new_thing, point(X, Y));
+        auto t = thing_new(new_thing, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Floor tile %s not found", tilename.c_str());
diff --git a/src/level_biome_common.cpp b/src/level_biome_common.cpp
index 7f60ee8f2..9402ab1ce 100644
--- a/src/level_biome_common.cpp
+++ b/src/level_biome_common.cpp
@@ -538,6 +538,10 @@ void Level::place_random_treasure(Dungeonp d)
       // Be nice and enchant this lost treasure.
       //
       auto t = thing_new(tp->name(), point(x, y));
+      if (! t) {
+        continue;
+      }
+
       if (pcg_random_range(0, 100) < 20) {
         t->enchant_randomly();
       }
diff --git a/src/level_biome_dungeon.cpp b/src/level_biome_dungeon.cpp
index 99b9533a3..62ffbba81 100644
--- a/src/level_biome_dungeon.cpp
+++ b/src/level_biome_dungeon.cpp
@@ -806,7 +806,11 @@ void Level::create_biome_dungeon_place_walls(Dungeonp d, Tpp tp, int variant, in
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Wall tile %s not found", tilename.c_str());
@@ -890,7 +894,11 @@ void Level::create_biome_dungeon_place_rocks(Dungeonp d, int variant, int block_
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Rock tile %s not found", tilename.c_str());
@@ -1006,7 +1014,10 @@ void Level::create_biome_dungeon_place_floors(Dungeonp d, std::string what, int
           cnt++;
         }
 
-        auto t    = thing_new(new_thing, point(X, Y));
+        auto t = thing_new(new_thing, point(X, Y));
+        if (! t) {
+          continue;
+        }
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Floor tile %s not found", tilename.c_str());
diff --git a/src/level_biome_flooded.cpp b/src/level_biome_flooded.cpp
index 3f73ffad0..e7c7823cc 100644
--- a/src/level_biome_flooded.cpp
+++ b/src/level_biome_flooded.cpp
@@ -598,7 +598,11 @@ void Level::create_biome_flooded_place_walls(Dungeonp d, Tpp tp, int variant, in
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Wall tile %s not found", tilename.c_str());
@@ -682,7 +686,11 @@ void Level::create_biome_flooded_place_rocks(Dungeonp d, int variant, int block_
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Rock tile %s not found", tilename.c_str());
@@ -798,7 +806,11 @@ void Level::create_biome_flooded_place_floors(Dungeonp d, std::string what, int
           cnt++;
         }
 
-        auto t    = thing_new(new_thing, point(X, Y));
+        auto t = thing_new(new_thing, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Floor tile %s not found", tilename.c_str());
diff --git a/src/level_biome_ice.cpp b/src/level_biome_ice.cpp
index 77d7dfbbe..363d9ecfa 100644
--- a/src/level_biome_ice.cpp
+++ b/src/level_biome_ice.cpp
@@ -455,7 +455,11 @@ void Level::create_biome_ice_place_rocks(Dungeonp d, int variant, int block_widt
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Rock tile %s not found", tilename.c_str());
@@ -755,7 +759,11 @@ void Level::create_biome_ice_place_floors(Dungeonp d, std::string what, int floo
           cnt++;
         }
 
-        auto t    = thing_new(new_thing, point(X, Y));
+        auto t = thing_new(new_thing, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Floor tile %s not found", tilename.c_str());
diff --git a/src/level_biome_lava.cpp b/src/level_biome_lava.cpp
index 5d191cea1..633d8b129 100644
--- a/src/level_biome_lava.cpp
+++ b/src/level_biome_lava.cpp
@@ -471,14 +471,20 @@ void Level::create_biome_lava_place_rocks(Dungeonp d, int variant, int block_wid
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
-        auto tile = tile_find(tilename);
-        if (unlikely(! tile)) {
-          ERR("Rock tile %s not found", tilename.c_str());
-          return;
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
         }
 
-        t->tile_curr = tile->global_index;
+        if (t) {
+          auto tile = tile_find(tilename);
+          if (unlikely(! tile)) {
+            ERR("Rock tile %s not found", tilename.c_str());
+            return;
+          }
+
+          t->tile_curr = tile->global_index;
+        }
       }
     }
   }
@@ -726,7 +732,11 @@ void Level::create_biome_lava_place_floors(Dungeonp d, std::string what, int flo
           cnt++;
         }
 
-        auto t    = thing_new(new_thing, point(X, Y));
+        auto t = thing_new(new_thing, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Floor tile %s not found", tilename.c_str());
diff --git a/src/level_biome_sewer.cpp b/src/level_biome_sewer.cpp
index f3c467e2f..c5072dd52 100644
--- a/src/level_biome_sewer.cpp
+++ b/src/level_biome_sewer.cpp
@@ -446,7 +446,11 @@ void Level::create_biome_sewer_place_walls(int variant, int block_width, int blo
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("wall tile %s not found", tilename.c_str());
diff --git a/src/level_biome_swamp.cpp b/src/level_biome_swamp.cpp
index 5ef255a44..b579d4ded 100644
--- a/src/level_biome_swamp.cpp
+++ b/src/level_biome_swamp.cpp
@@ -373,7 +373,11 @@ void Level::create_biome_swamp_place_rocks(Dungeonp d, int variant, int block_wi
           cnt++;
         }
 
-        auto t    = thing_new(what, point(X, Y));
+        auto t = thing_new(what, point(X, Y));
+        if (! t) {
+          continue;
+        }
+
         auto tile = tile_find(tilename);
         if (unlikely(! tile)) {
           ERR("Rock tile %s not found", tilename.c_str());
diff --git a/src/level_create.cpp b/src/level_create.cpp
index c1d9044b7..e50cf1918 100644
--- a/src/level_create.cpp
+++ b/src/level_create.cpp
@@ -114,7 +114,9 @@ void Level::create(point3d world_at, point grid_at, uint32_t seed, int difficult
     } else {
       cursor = thing_new("cursor", player->curr_at);
     }
-    cursor->hide();
+    if (cursor) {
+      cursor->hide();
+    }
     is_map_mini_valid = true;
   }
 
diff --git a/src/level_map_update.cpp b/src/level_map_update.cpp
index 0a94554e2..966260f06 100644
--- a/src/level_map_update.cpp
+++ b/src/level_map_update.cpp
@@ -73,8 +73,10 @@ void Level::update_water_next_to_lava(bool &changed)
                   if (! is_starting) {
                     if (! is_steam(x, y)) {
                       auto steam = thing_new("steam", point(x, y));
-                      changed    = true;
-                      steam->lifespan_set(pcg_random_range(1, 10));
+                      if (steam) {
+                        changed = true;
+                        steam->lifespan_set(pcg_random_range(1, 10));
+                      }
                     }
                   }
                 }
@@ -101,8 +103,10 @@ void Level::update_water_next_to_lava(bool &changed)
                   if (! is_starting) {
                     if (! is_steam(x, y)) {
                       auto steam = thing_new("steam", point(x, y));
-                      changed    = true;
-                      steam->lifespan_set(pcg_random_range(1, 10));
+                      if (steam) {
+                        changed = true;
+                        steam->lifespan_set(pcg_random_range(1, 10));
+                      }
                     }
                   }
                 }
diff --git a/src/my_py_thing.hpp b/src/my_py_thing.hpp
index bde9543ed..43c60545f 100644
--- a/src/my_py_thing.hpp
+++ b/src/my_py_thing.hpp
@@ -451,6 +451,7 @@ PyObject *thing_is_obs_wall_or_door(PyObject *obj, PyObject *args, PyObject *key
 PyObject *thing_is_obs_when_dead(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_ogre(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_on_fire(PyObject *obj, PyObject *args, PyObject *keywds);
+PyObject *thing_is_only_one_per_tile(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_openable(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_organic(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_pack(PyObject *obj, PyObject *args, PyObject *keywds);
@@ -562,7 +563,6 @@ PyObject *thing_is_unused_flag137(PyObject *obj, PyObject *args, PyObject *keywd
 PyObject *thing_is_unused_flag138(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_unused_flag139(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_unused_flag13(PyObject *obj, PyObject *args, PyObject *keywds);
-PyObject *thing_is_unused_flag140(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_unused_flag142(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_unused_flag14(PyObject *obj, PyObject *args, PyObject *keywds);
 PyObject *thing_is_unused_flag15(PyObject *obj, PyObject *args, PyObject *keywds);
diff --git a/src/my_py_tp.hpp b/src/my_py_tp.hpp
index 51b0c21c6..a9d0e55d6 100644
--- a/src/my_py_tp.hpp
+++ b/src/my_py_tp.hpp
@@ -536,6 +536,7 @@ TP_SET_PROTO(is_obs_throwing)
 TP_SET_PROTO(is_obs_wall_or_door)
 TP_SET_PROTO(is_obs_when_dead)
 TP_SET_PROTO(is_ogre)
+TP_SET_PROTO(is_only_one_per_tile)
 TP_SET_PROTO(is_openable)
 TP_SET_PROTO(is_organic)
 TP_SET_PROTO(is_pillar)
@@ -652,7 +653,6 @@ TP_SET_PROTO(is_unused_flag137)
 TP_SET_PROTO(is_unused_flag138)
 TP_SET_PROTO(is_unused_flag139)
 TP_SET_PROTO(is_unused_flag14)
-TP_SET_PROTO(is_unused_flag140)
 TP_SET_PROTO(is_unused_flag142)
 TP_SET_PROTO(is_unused_flag15)
 TP_SET_PROTO(is_unused_flag16)
diff --git a/src/my_thing.hpp b/src/my_thing.hpp
index afbf51adb..e4e0d9273 100644
--- a/src/my_thing.hpp
+++ b/src/my_thing.hpp
@@ -1629,6 +1629,7 @@ typedef class Thing_
   int is_obs_wall_or_door(void);
   int is_obs_when_dead(void);
   int is_ogre(void);
+  int is_only_one_per_tile(void);
   int is_openable(void);
   int is_organic(void);
   int is_pillar(void);
@@ -1740,7 +1741,6 @@ typedef class Thing_
   int is_unused_flag138(void);
   int is_unused_flag139(void);
   int is_unused_flag13(void);
-  int is_unused_flag140(void);
   int is_unused_flag142(void);
   int is_unused_flag14(void);
   int is_unused_flag15(void);
diff --git a/src/my_thing_template.hpp b/src/my_thing_template.hpp
index 741080067..d10061492 100644
--- a/src/my_thing_template.hpp
+++ b/src/my_thing_template.hpp
@@ -553,6 +553,7 @@ class Tp
   int _is_obs_wall_or_door {};
   int _is_obs_when_dead {};
   int _is_ogre {};
+  int _is_only_one_per_tile {};
   int _is_openable {};
   int _is_organic {};
   int _is_pillar {};
@@ -666,7 +667,6 @@ class Tp
   int _is_unused_flag138 {};
   int _is_unused_flag139 {};
   int _is_unused_flag14 {};
-  int _is_unused_flag140 {};
   int _is_unused_flag142 {};
   int _is_unused_flag15 {};
   int _is_unused_flag16 {};
@@ -1863,6 +1863,7 @@ class Tp
   int is_obs_wall_or_door(void) const;
   int is_obs_when_dead(void) const;
   int is_ogre(void) const;
+  int is_only_one_per_tile(void) const;
   int is_openable(void) const;
   int is_organic(void) const;
   int is_pillar(void) const;
@@ -1974,7 +1975,6 @@ class Tp
   int is_unused_flag138(void) const;
   int is_unused_flag139(void) const;
   int is_unused_flag13(void) const;
-  int is_unused_flag140(void) const;
   int is_unused_flag142(void) const;
   int is_unused_flag14(void) const;
   int is_unused_flag15(void) const;
@@ -2612,6 +2612,7 @@ class Tp
   void is_obs_wall_or_door_set(int v);
   void is_obs_when_dead_set(int v);
   void is_ogre_set(int v);
+  void is_only_one_per_tile_set(int v);
   void is_openable_set(int v);
   void is_organic_set(int v);
   void is_pillar_set(int v);
@@ -2723,7 +2724,6 @@ class Tp
   void is_unused_flag138_set(int v);
   void is_unused_flag139_set(int v);
   void is_unused_flag13_set(int v);
-  void is_unused_flag140_set(int v);
   void is_unused_flag142_set(int v);
   void is_unused_flag14_set(int v);
   void is_unused_flag15_set(int v);
diff --git a/src/py_thing_get.cpp b/src/py_thing_get.cpp
index 3f9d29765..7205d43b8 100644
--- a/src/py_thing_get.cpp
+++ b/src/py_thing_get.cpp
@@ -472,6 +472,7 @@ THING_BODY_GET_BOOL(thing_is_obs_wall_or_door, is_obs_wall_or_door)
 THING_BODY_GET_BOOL(thing_is_obs_when_dead, is_obs_when_dead)
 THING_BODY_GET_BOOL(thing_is_ogre, is_ogre)
 THING_BODY_GET_BOOL(thing_is_on_fire, is_on_fire)
+THING_BODY_GET_BOOL(thing_is_only_one_per_tile, is_only_one_per_tile)
 THING_BODY_GET_BOOL(thing_is_openable, is_openable)
 THING_BODY_GET_BOOL(thing_is_organic, is_organic)
 THING_BODY_GET_BOOL(thing_is_pack, is_monst_pack)
@@ -583,7 +584,6 @@ THING_BODY_GET_BOOL(thing_is_unused_flag137, is_unused_flag137)
 THING_BODY_GET_BOOL(thing_is_unused_flag138, is_unused_flag138)
 THING_BODY_GET_BOOL(thing_is_unused_flag139, is_unused_flag139)
 THING_BODY_GET_BOOL(thing_is_unused_flag13, is_unused_flag13)
-THING_BODY_GET_BOOL(thing_is_unused_flag140, is_unused_flag140)
 THING_BODY_GET_BOOL(thing_is_unused_flag142, is_unused_flag142)
 THING_BODY_GET_BOOL(thing_is_unused_flag14, is_unused_flag14)
 THING_BODY_GET_BOOL(thing_is_unused_flag15, is_unused_flag15)
diff --git a/src/py_tp.cpp b/src/py_tp.cpp
index 2b0e3daa2..ba6fdb2f1 100644
--- a/src/py_tp.cpp
+++ b/src/py_tp.cpp
@@ -1233,6 +1233,7 @@ TP_BODY_SET_INT(is_obs_throwing)
 TP_BODY_SET_INT(is_obs_wall_or_door)
 TP_BODY_SET_INT(is_obs_when_dead)
 TP_BODY_SET_INT(is_ogre)
+TP_BODY_SET_INT(is_only_one_per_tile)
 TP_BODY_SET_INT(is_openable)
 TP_BODY_SET_INT(is_organic)
 TP_BODY_SET_INT(is_pillar)
@@ -1346,7 +1347,6 @@ TP_BODY_SET_INT(is_unused_flag137)
 TP_BODY_SET_INT(is_unused_flag138)
 TP_BODY_SET_INT(is_unused_flag139)
 TP_BODY_SET_INT(is_unused_flag14)
-TP_BODY_SET_INT(is_unused_flag140)
 TP_BODY_SET_INT(is_unused_flag142)
 TP_BODY_SET_INT(is_unused_flag15)
 TP_BODY_SET_INT(is_unused_flag16)
diff --git a/src/python_methods.cpp b/src/python_methods.cpp
index 55a60f8d5..1014eef9e 100644
--- a/src/python_methods.cpp
+++ b/src/python_methods.cpp
@@ -704,6 +704,7 @@ static PyMethodDef python_c_METHODS[] = {
     MY_ADD_PYTHON_FUNCTION(thing_is_obs_when_dead),
     MY_ADD_PYTHON_FUNCTION(thing_is_ogre),
     MY_ADD_PYTHON_FUNCTION(thing_is_on_fire),
+    MY_ADD_PYTHON_FUNCTION(thing_is_only_one_per_tile),
     MY_ADD_PYTHON_FUNCTION(thing_is_openable),
     MY_ADD_PYTHON_FUNCTION(thing_is_organic),
     MY_ADD_PYTHON_FUNCTION(thing_is_pack),
@@ -817,7 +818,6 @@ static PyMethodDef python_c_METHODS[] = {
     MY_ADD_PYTHON_FUNCTION(thing_is_unused_flag138),
     MY_ADD_PYTHON_FUNCTION(thing_is_unused_flag139),
     MY_ADD_PYTHON_FUNCTION(thing_is_unused_flag14),
-    MY_ADD_PYTHON_FUNCTION(thing_is_unused_flag140),
     MY_ADD_PYTHON_FUNCTION(thing_is_unused_flag142),
     MY_ADD_PYTHON_FUNCTION(thing_is_unused_flag15),
     MY_ADD_PYTHON_FUNCTION(thing_is_unused_flag16),
@@ -1542,6 +1542,7 @@ static PyMethodDef python_c_METHODS[] = {
     MY_ADD_PYTHON_TP_FUNCTION(is_obs_wall_or_door),
     MY_ADD_PYTHON_TP_FUNCTION(is_obs_when_dead),
     MY_ADD_PYTHON_TP_FUNCTION(is_ogre),
+    MY_ADD_PYTHON_TP_FUNCTION(is_only_one_per_tile),
     MY_ADD_PYTHON_TP_FUNCTION(is_openable),
     MY_ADD_PYTHON_TP_FUNCTION(is_organic),
     MY_ADD_PYTHON_TP_FUNCTION(is_pillar),
@@ -1655,7 +1656,6 @@ static PyMethodDef python_c_METHODS[] = {
     MY_ADD_PYTHON_TP_FUNCTION(is_unused_flag138),
     MY_ADD_PYTHON_TP_FUNCTION(is_unused_flag139),
     MY_ADD_PYTHON_TP_FUNCTION(is_unused_flag14),
-    MY_ADD_PYTHON_TP_FUNCTION(is_unused_flag140),
     MY_ADD_PYTHON_TP_FUNCTION(is_unused_flag142),
     MY_ADD_PYTHON_TP_FUNCTION(is_unused_flag15),
     MY_ADD_PYTHON_TP_FUNCTION(is_unused_flag16),
diff --git a/src/thing_api.cpp b/src/thing_api.cpp
index e50afe112..637f9a294 100644
--- a/src/thing_api.cpp
+++ b/src/thing_api.cpp
@@ -895,10 +895,10 @@ int Thing::is_unused_flag139(void)
   TRACE_NO_INDENT();
   return (tp()->is_unused_flag139());
 }
-int Thing::is_unused_flag140(void)
+int Thing::is_only_one_per_tile(void)
 {
   TRACE_NO_INDENT();
-  return (tp()->is_unused_flag140());
+  return (tp()->is_only_one_per_tile());
 }
 int Thing::is_unused_flag142(void)
 {
diff --git a/src/thing_init.cpp b/src/thing_init.cpp
index 07ecfdb39..dbb595c89 100644
--- a/src/thing_init.cpp
+++ b/src/thing_init.cpp
@@ -16,6 +16,7 @@ Thingp Level::thing_new(Tpp tp, const point at, Thingp owner)
     err("No tp provided for thing creation");
     return nullptr;
   }
+
   return thing_new(tp->name(), at, owner);
 }
 
@@ -26,6 +27,25 @@ Thingp Level::thing_new(const std::string &tp_name, Thingp owner)
 
 Thingp Level::thing_new(const std::string &name, const point at, Thingp owner)
 {
+  auto tp = tp_find(name);
+  if (! tp) {
+    return nullptr;
+  }
+
+  //
+  // Ensure things like chasms don't pile up on the same tile.
+  //
+  if (tp->is_only_one_per_tile()) {
+    FOR_ALL_THINGS_AT_DEPTH(this, o, at.x, at.y, tp->z_depth)
+    {
+      if (o->tp() == tp) {
+        dbg("Do not create %s as already exist at %s", name.c_str(), at.to_string().c_str());
+        return nullptr;
+      }
+    }
+    FOR_ALL_THINGS_END()
+  }
+
   auto t = new class Thing_();
   t->init(this, name, at, owner);
   return t;
diff --git a/src/thing_match.cpp b/src/thing_match.cpp
index 327e2d99b..25a75a24f 100644
--- a/src/thing_match.cpp
+++ b/src/thing_match.cpp
@@ -355,6 +355,7 @@ bool Tp::matches(const std::string &what)
   if (is_obs_wall_or_door() && (what == "is_obs_wall_or_door")) { return true; }
   if (is_obs_when_dead() && (what == "is_obs_when_dead")) { return true; }
   if (is_ogre() && (what == "is_ogre")) { return true; }
+  if (is_only_one_per_tile() && (what == "is_only_one_per_tile")) { return true; }
   if (is_openable() && (what == "is_openable")) { return true; }
   if (is_organic() && (what == "is_organic")) { return true; }
   if (is_pillar() && (what == "is_pillar")) { return true; }
@@ -462,7 +463,6 @@ bool Tp::matches(const std::string &what)
   if (is_unused_flag138() && (what == "is_unused_flag138")) { return true; }
   if (is_unused_flag139() && (what == "is_unused_flag139")) { return true; }
   if (is_unused_flag13() && (what == "is_unused_flag13")) { return true; }
-  if (is_unused_flag140() && (what == "is_unused_flag140")) { return true; }
   if (is_unused_flag142() && (what == "is_unused_flag142")) { return true; }
   if (is_unused_flag14() && (what == "is_unused_flag14")) { return true; }
   if (is_unused_flag15() && (what == "is_unused_flag15")) { return true; }
@@ -958,6 +958,7 @@ bool Thing::matches(const std::string &what)
   if (is_obs_wall_or_door() && (what == "is_obs_wall_or_door")) { return true; }
   if (is_obs_when_dead() && (what == "is_obs_when_dead")) { return true; }
   if (is_ogre() && (what == "is_ogre")) { return true; }
+  if (is_only_one_per_tile() && (what == "is_only_one_per_tile")) { return true; }
   if (is_openable() && (what == "is_openable")) { return true; }
   if (is_organic() && (what == "is_organic")) { return true; }
   if (is_pillar() && (what == "is_pillar")) { return true; }
@@ -1066,7 +1067,6 @@ bool Thing::matches(const std::string &what)
   if (is_unused_flag138() && (what == "is_unused_flag138")) { return true; }
   if (is_unused_flag139() && (what == "is_unused_flag139")) { return true; }
   if (is_unused_flag13() && (what == "is_unused_flag13")) { return true; }
-  if (is_unused_flag140() && (what == "is_unused_flag140")) { return true; }
   if (is_unused_flag142() && (what == "is_unused_flag142")) { return true; }
   if (is_unused_flag14() && (what == "is_unused_flag14")) { return true; }
   if (is_unused_flag15() && (what == "is_unused_flag15")) { return true; }
@@ -1551,6 +1551,7 @@ std::function< int(Thingp) > Thing::matches_to_func(const std::string &what)
   if (what == "is_obs_wall_or_door") { return &Thing::is_obs_wall_or_door; }
   if (what == "is_obs_when_dead") { return &Thing::is_obs_when_dead; }
   if (what == "is_ogre") { return &Thing::is_ogre; }
+  if (what == "is_only_one_per_tile") { return &Thing::is_only_one_per_tile; }
   if (what == "is_openable") { return &Thing::is_openable; }
   if (what == "is_organic") { return &Thing::is_organic; }
   if (what == "is_pillar") { return &Thing::is_pillar; }
@@ -1658,7 +1659,6 @@ std::function< int(Thingp) > Thing::matches_to_func(const std::string &what)
   if (what == "is_unused_flag138") { return &Thing::is_unused_flag138; }
   if (what == "is_unused_flag139") { return &Thing::is_unused_flag139; }
   if (what == "is_unused_flag13") { return &Thing::is_unused_flag13; }
-  if (what == "is_unused_flag140") { return &Thing::is_unused_flag140; }
   if (what == "is_unused_flag142") { return &Thing::is_unused_flag142; }
   if (what == "is_unused_flag14") { return &Thing::is_unused_flag14; }
   if (what == "is_unused_flag15") { return &Thing::is_unused_flag15; }
diff --git a/src/thing_template_fn.cpp b/src/thing_template_fn.cpp
index 1da0ecd7a..6e65103d0 100644
--- a/src/thing_template_fn.cpp
+++ b/src/thing_template_fn.cpp
@@ -638,6 +638,7 @@ int Tp::is_obs_throwing(void) const { return _is_obs_throwing; }
 int Tp::is_obs_wall_or_door(void) const { return _is_obs_wall_or_door; }
 int Tp::is_obs_when_dead(void) const { return _is_obs_when_dead; }
 int Tp::is_ogre(void) const { return _is_ogre; }
+int Tp::is_only_one_per_tile(void) const { return _is_only_one_per_tile; }
 int Tp::is_openable(void) const { return _is_openable; }
 int Tp::is_organic(void) const { return _is_organic; }
 int Tp::is_pillar(void) const { return _is_pillar; }
@@ -749,7 +750,6 @@ int Tp::is_unused_flag137(void) const { return _is_unused_flag137; }
 int Tp::is_unused_flag138(void) const { return _is_unused_flag138; }
 int Tp::is_unused_flag139(void) const { return _is_unused_flag139; }
 int Tp::is_unused_flag13(void) const { return _is_unused_flag13; }
-int Tp::is_unused_flag140(void) const { return _is_unused_flag140; }
 int Tp::is_unused_flag142(void) const { return _is_unused_flag142; }
 int Tp::is_unused_flag14(void) const { return _is_unused_flag14; }
 int Tp::is_unused_flag15(void) const { return _is_unused_flag15; }
@@ -1387,6 +1387,7 @@ void Tp::is_obs_throwing_set(int v) { _is_obs_throwing = v; }
 void Tp::is_obs_wall_or_door_set(int v) { _is_obs_wall_or_door = v; }
 void Tp::is_obs_when_dead_set(int v) { _is_obs_when_dead = v; }
 void Tp::is_ogre_set(int v) { _is_ogre = v; }
+void Tp::is_only_one_per_tile_set(int v) { _is_only_one_per_tile = v; }
 void Tp::is_openable_set(int v) { _is_openable = v; }
 void Tp::is_organic_set(int v) { _is_organic = v; }
 void Tp::is_pillar_set(int v) { _is_pillar = v; }
@@ -1498,7 +1499,6 @@ void Tp::is_unused_flag137_set(int v) { _is_unused_flag137 = v; }
 void Tp::is_unused_flag138_set(int v) { _is_unused_flag138 = v; }
 void Tp::is_unused_flag139_set(int v) { _is_unused_flag139 = v; }
 void Tp::is_unused_flag13_set(int v) { _is_unused_flag13 = v; }
-void Tp::is_unused_flag140_set(int v) { _is_unused_flag140 = v; }
 void Tp::is_unused_flag142_set(int v) { _is_unused_flag142 = v; }
 void Tp::is_unused_flag14_set(int v) { _is_unused_flag14 = v; }
 void Tp::is_unused_flag15_set(int v) { _is_unused_flag15 = v; }