A nightmare, u, is a type of monster that appears in SporkHack and EvilHack - in Hack'EM, the monster is known as a greater nightmare. Nightmares are herbivorous domestic monsters that serve as the chaotic equivalent of the horse in the unicorn or horse monster class: they possess most of the same qualities and share the same attacks, but their bite is poisonous and they also possess poison resistance.
By a route obscure and lonely,
Haunted by ill angels only,
Where an Eidolon, named NIGHT,
On a black throne reigns upright,
I have reached these lands but newly
From an ultimate dim Thule--
From a wild weird clime that lieth, sublime,
Out of SPACE -- Out of TIME.
[ Dream-Land, by Edgar Allen Poe ]