Nightmare (SLASH'EM)

u Nightmare
Difficulty	17
Attacks	Head butt 3d12, Kick 3d6

u Nightmare
Difficulty	17
Attacks	Head butt 3d12, Kick 3d6
Base level	12
Base experience	386
Speed	24
Base AC	-2
Base MR	70
Alignment	15 (lawful)
Frequency (by normal means)	Unique
Genocidable	No
Weight	1500
Nutritional value	300
Size	Large
Resistances	poison, fire, cold, electricity
Resistances conveyed	None
Nightmare: has no hands. is an animal. is herbivorous. is not a valid polymorphable form. is female. is normally generated hostile. wanders randomly. can follow you to other levels. is nasty. is strong. wants the Amulet of Yendor, the Bell of Opening, the Book of the Dead, the Candelabrum of Invocation, and your quest artifact. never leaves a corpse. hits creatures as a +2 weapon.
Reference	SLASH'EM_0.0.7E7F2/monst.c#line4568

Nightmare is a monster added in SLASH'EM. She is the Lawful Quest nemesis, and will leave the Key of Law when killed and Nighthorn if killed in a way that would leave a corpse - Nightmare will never leave a corpse, instead simply producing Nighthorn and the message "All that remains is her horn...". Like all alignment quest nemesises, Nightmare is covetous and will teleport to your position once awakened. Nighthorn is not strictly a unicorn, and thus will not accept gems nor use her horn to heal herself. As Nighthorn grants reflection, Nightmare herself has reflection and all beams will reflect off of her horn.

Nightmare is also found in the dNethack Chaos Quest, with slight changes. She is now a black (chaotic) unicorn, and will be peaceful to chaotics. If they want the slightly modified horn, they'll have to take the -5 penalty for killing a coaligned unicorn. See the Nighthorn article for more.