The
Book of the
Dead is also one of the
NetHack Invocation Artifacts, possession and uncursement of which is required to obtain the
Amulet of Yendor. You receive the Book of the Dead by defeating the
Wizard of Yendor (even though he comes back to life
ad nauseam, you still get the Book).
If the Book is blessed, reading it makes all undead around you become peaceful. Undead sharing your alignment will become tame instead (imagine that!). If the Book is uncursed, you get an ominous message but nothing actually happens.
If the Book is cursed, some undead will be summoned. This includes a 1/3 chance (modified by luck, etc) of placing a lich or a nalfeshnee next to you, animating any corpses you are carrying, and then summoning some random undead creatures around you. Don't do this.