Demilich

A Demilich is a mob that rarely appears in Spawners in Gold and Diamond Dungeons and very rarely spawns elsewhere. They have the appearance of a half-rotten skeleton in a damaged cloak. They refuse to engage in melee. Instead, they summon Skeletal Minions to do their fighting for them. They have 24 health (12 hearts) and drop 0-1 bones, 0-1 rotten flesh, 0-1 leather cap (heavily damaged), and 7 experience when defeated. Both the Demilich and its minions are undead, although the Demilich is fireproof due to its cloak.

Skeletal Minions
Skeletal Minions are what the Demilich summons instead of fighting the player directly. These minions have 16 health (8 hearts), travel slightly faster than the Zombie. They deal 1.5 damage (0.75 hearts) on Easy, 2.25 damage (1.125 hearts) on Medium, and 3 damage (1.5 hearts) on Hard. They drop 0-2 bones and 3 experience when defeated.