Minecraft wiki entry for Development_versions, associated text: Added as an end-game challenge, or mini-boss.
Will always drop a totem of undying upon death. May drop emeralds too.
In battle, they will summon vexes and fangs to attack.
Raise their arms when casting a spell.
Fangs always deal 6 damage, ignoring armor.
Hostile towards players and villagers.
Spawn in the two upper floors of woodland mansions upon generation. They will not respawn.
Will change any blue colored sheep in a radius of 16 blocks into red.