, quest nemeses and demon lords are difficult to kill
because they keep teleport
ing away to heal themselves. If you can't
kill them instantly (for example, with a wand of death
corpse), you need to find a way to make them stand still
and fight you.
The technique for doing this is known as the upstairs/downstairs
trick. It begins with noticing that these monsters teleport to the up
staircase. If you can get there before they do, they won't teleport
away. If you can't, you'll need to exploit another feature of these
monsters: they'll follow you up or down stairs if they are next to
you. This enables the following strategy:
- Head for the nearest staircase. If the monster is there, fight
him until he moves away. If he goes up or down the stairs, follow
him. Otherwise, just occupy the staircase yourself.
- You should now be on a staircase on the same level as the
monster. If it's an up staircase, you're done - he can't teleport
away, so just kill him.
- If it's a down staircase, wait for the monster to come back. As
soon as he's next to you, go downstairs.
- If you're on the up staircase now, fine. If not, go back to step
1 - fight the monster until he either moves away from the staircase or
runs up it.
Sadly, this technique does not work against master liches and
arch-liches, because they do not follow you up or down stairs. I'd
advise genociding them or petrifying them with cockatrice eggs.