Undead

Undead in NetHack are a class of unliving monsters. They include all liches L, mummies M, vampires V, wraiths and barrow wights W, zombies Z, ghosts, and shades.

Undead take extra d4 from blessed items, and vampires and shades take an extra d20 from silver weapons. Drinking holy water also harms them; however, unholy water actually exercises their constitution.

Priests and knights can turn undead, which can make them flee or destroy the low-level ones completely. A wand of undead turning has a similar effect.

Undead are immune to level drain, such as from the Staff of Aesculapius. They're also all immune to Cold, Sleep, and Poison.

Reading the Book of the Dead while cursed will summon (hostile) undead, while a blessed book will calm and even possibly tame them. If nothing else helps, the Sunsword does double damage against undead.