The Coffin of Necromancy is a new craftable item in Elona+ from the pot for fusion. Using it will summon an undead ally that follows the player and kills hostile creatures. The undead can be put back in its coffin and there is no limit on the number of times it can be reused. Note that while you can give items to zombies, any such items will be lost, as you can't take items from a zombie, and they don't drop any items when returned to its coffin. The type of zombie depends on the worth of the monster part added in the Necromancy recipe in the Pot for fusion.