Last one of these for now. Last 3 mobs! (Making the 3 that win into an addon)
Mob 1) The Warped Wallow.
Spawning in the depths of the nether, hidden in the blue fungus trees of the Warped Forest, the Warped Wallow is a very useful mob. It is the only cold thing in the nether, and is useful in multiple ways. Tame it with a nether wart and it will follow you around, it will throw snowballs at hostile mobs that will actually damage fire based mobs like magma cubes and blaze, but will not attempt to attack endermen. It will also throw snowballs at the player if the player is on fire to put the player out. A good utility mob in fortresses!
Mob 2) The Watcher.
Spawning within the walls of ancient cities, strongholds, bastions, end cities, and nether fortresses, the Watchers are a neutral mob that will sit dormant with it's eye closed. Every so often it will open its eye and anything in it's line of sight will be given VERY strong fatal poison. It blends in with all kinds of brick and will spawn in all structures with bricks. Will also poison mobs, and is immune to most damage types. Mine it with a pickaxe to kill it.
Mob 3) the Adventurer.
A new sort of wandering trader, the adventurer will appear near temple structures like desert temples ruined portals and jungle temples. It will offer high value items for high cost, at limited amounts. Such as enchanted apples, netherite, totems, Sculk, and music discs! A good late game trader! (Note: this trader does not lower it's prices for the hero of the village effect and can not be zombified)