A ghoul mage is a monster in SLASH'EM. It is able to cast spells up to curse items, and occasionally aggravate monster, as well as doing a small amount of physical damage. Note that, unlike most other Z, it is not mindless, and can be detected via telepathy.
These are not very dangerous, but they can be a great annoyance, mostly because they are very fond of cursing your items, since they cannot cast that many other spells. If you don't have a convenient way of uncursing or protecting your items (such as Magicbane or a spellbook of remove curse, they should be given a high priority for destruction, and may even be worth a scroll of genocide.
The forces of the gloom know each other, and are strangely
balanced by each other. Teeth and claws fear what they cannot
grasp. Blood-drinking bestiality, voracious appetites, hunger
in search of prey, the armed instincts of nails and jaws which
have for source and aim the belly, glare and smell out
uneasily the impassive spectral forms straying beneath a
shroud, erect in its vague and shuddering robe, and which seem
to them to live with a dead and terrible life. These
brutalities, which are only matter, entertain a confused fear
of having to deal with the immense obscurity condensed into an
unknown being. A black figure barring the way stops the wild
beast short. That which emerges from the cemetery intimidates
and disconcerts that which emerges from the cave; the
ferocious fear the sinister; wolves recoil when they encounter