Features Added to Combat

Offhand Attacks (only for Daggers, Sickles and Gauntlets):

Right-clicking with a dagger, sickle or gauntlet in your off-hand will allow you to attack with it.

Note that Offhand Attacks do not activate the ability of the offhand weapon, and in a handful of circumstances will actually activate the ability of your mainhand weapon. If your mainhand's ability has activated during an offhand attack, please do not report it as an issue because there's simply not much I can do about it - in its current state, Minecraft is not designed for handling offhand melee attacks accurately.

Long Reach Attacks (only for Spears, Glaives and Whips):

You can hit enemies with a spear, glaive or whip from up to 5 blocks away. In 1.16+, the attack indicator will properly match this distance. In 1.15.2, the attack indicator will not match up, but you will still be able to attack from this distance anyway.

Dual-Wielding Crossbows (only for the Dual Crossbow and its unique variants)

If you have a Dual Wield Crossbow (or a variant of it) in both of your hands, you will load and fire both at the same time, consuming 2x ammo for 2x arrow output. This works best with mods that remove temporary immunity after receiving damage. Note that only the mainhand crossbow will be rendered during loading and firing.