An elf is a very rare monster — it is not randomly generated, nor placed anywhere in a normal game. An elf can be created by zapping a wand of undead turning at an elf corpse. They can also be created by reverse genocide, if the player is elven.
It should be noted that the elf monster has a higher difficulty than the other monsters associated with a race, being on a par with the player monsters. This may be related to the fact that elf used to be a role.
Encyclopedia entry Edit
The Elves sat round the fire upon the grass or upon the sawn
rings of old trunks. Some went to and fro bearing cups and
pouring drinks; others brought food on heaped plates and
"This is poor fare," they said to the hobbits; "for we are
lodging in the greenwood far from our halls. If ever you are
our guests at home, we will treat you better."
"It seems to me good enough for a birthday-party," said Frodo.
Pippin afterwards recalled little of either food or drink, for
his mind was filled with the light upon the elf-faces, and the
sound of voices so various and so beautiful that he felt in a
waking dream. [...]
Sam could never describe in words, nor picture clearly to
himself, what he felt or thought that night, though it remained
in his memory as one of the chief events of his life. The
nearest he ever got was to say: "Well, sir, if I could grow
apples like that, I would call myself a gardener. But it was
the singing that went to my heart, if you know what I mean."