Torch Fire Config is no longer a boolean, but an integer. Its now a percent chance of setting entities on fire, with 0 disabling the mechanic.
The time an entity is set on fire by being punched with a torch is now configurable
Increased default value of "minMobArrowAmount" to 16 and "extraMobArrowAmount" to 48.
Ghasts are now actually incorporeal as Mojang keeps describing them.
Being 3 blocks around lava will set entities on fire due to convection.
If a Drowned is out of water, and rain, and is in a hot biome, they will convert into regular Zombies after a short amount of time.
Drowned will instantly extinguish themselves from fire as they are constantly wet.
Naming a wolf "Princess" or "Cupcake" will cause them to be hostile towards children.
Endermen are no longer racist against players and will now attack any mob, that's not another Enderman or wearing a Carved Pumpkin on their head, that stares at their eyes.