jls (09/15/82)
The Drain Life staff will do the job if you have enough hit points. You need
at least twice that which is necessary to kill the Umber. A staff of polymorph
can help too if you morph him into something "easy". Both of these staffs will
work even when you are confused. In fact if you zap ("z") a Drain Life, the
program will apply it to all monsters in the room and with enough hit points
you can kill more than one monster with one zap.
Good armor helps too. In a recent game I had AC of -6, 117 hp, an 8 time
enchanted two handed sword (yes, someone set it up with the wizards password),
but only a strength of 13. I had no trouble with Xorns, they could hit me, and
not much trouble with Umbers even when they confused me. The Umbers could hit
less than half the time and by randomly bumping into them I managed to kill
them. The Umbers aren't really that hard to kill if you can hit them and
withstand their hits.
I believe they can confuse within 3 spaces. A staff of cancellation inhibits
a particular Umbers ability to confuse. I've also been told that a ring of
Protection reduces the chances that the special attributes of some monsters
(Ants, Umbers, Rust monsters) will affect you.