The levels and stats will be a json in the config folder

Wither

Add PBWither, a child of Wither that has custom ai.
Summoning a vanilla wither replaces it with a Level 0 PBWither (Wither I).
By default there are 4 wither levels I, II, III, IV (corresponding roughly to the v3 difficulty 0, 2.66, 5.32, 8).
Make "dangerous" skulls slower but actually dangerous.
When the Wither is killed has 60% to drop a corrupted soul sand with one level higher corruption (So Wither I will drop corrupted II soulsand) or 40% chance to drop a corrupted soul sand of the same level as the Wither.
When the wither summons minions he goes into the shield mode for a few seconds?
When the Wither drops below half health he can only heal up to half health
Consume a Nether star to upgrade the corrupted soul sand
When Wither's low, minions should go near him to he can heal.
Make wither effect duration configurable per difficulty
rename resistances_weaknesses to resistances
Rework minions enchantments to be configurable
Make minions health configurable
Make charge knockback configurable
Make charge decide the target when becoming purple instead of when charging
Draft an attack where grabs the player to lift it up in the sky and let it fall

Ender Dragon

Add PBEnderDragon? This seems a looong shot. Maybe just keep the vanilla dragon with the current difficulty changes.
By default there are 4 Dragon levels I, II, III, IV (corresponding roughly to the v3 difficulty 0, 2.66, 5.32, 8).
When the dragon is killed she drops a corrupted end crystal to let you summon a higher difficulty one.

Elder Guardian

• To make a trident a Prismarine rod is required which is made with 2 blocks of prismarine

Warden

It's not a boss, stop asking for changes