The wand of death is arguably the most powerful wand in the game, but also quite dangerous. The spellbook with respective powers is the Spellbook of finger of death. One of the major sources of YASDs is the fabled Gnome With the Wand of Death.
Zapping it sends a ray of death towards an enemy, who will instantly die if not Death, magic resistant, reflecting, a demon, or nonliving. The same criteria apply to the player character. As with all wands, however, there is a chance that the wand will miss the target. "A death ray whizzes by you!" If you are being targeted with death rays, you should consider using some escape item unless you have reflection or magic resistance.
Zapping a wand of death at Death makes him stronger.
Zapping a wand of death at yourself results in an instadeath, even if you have magic resistance and/or reflection ("You irradiate yourself with pure energy!"). This is generally considered a Bad Idea. Beware also of bouncing rays.
The wand of death shares its base cost of 500 with the wand of wishing.
Wands comprise 4% of all randomly-generated items in the main dungeon, 6% in containers, 5% on the Rogue level, and 8% in Gehennom. There is a .5% chance that a randomly-generated wand will be a wand of death, making it one of the least generated wands. Orcus is guaranteed one, while all other monsters with difficulty of 8 or more can receive it as an offensive item if they're eligible for one.
In SporkHack, death rays will still cause damage and reduce your maximum hit points if you have magic resistance or reflection. If you have both, the damage is dramatically reduced and you lose much less maximum HP.