Tame ghouls eat only "old" corpses.
While they are sickness resistant, they are unfortunately far too weak to realistically against Pestilence or Demogorgon. An illiterate player who is throne farming might consider polymorphing into a ghoul, wearing an amulet of unchanging, and using a cursed unicorn horn as a source of confusion. Doing so obviously breaks polyselfless conduct, however.
Ghouls are part of the folklore of undead creatures. It originates from the Arabic "ghul", an evil spirit.
The depiction and properties can vary. They may be portrayed as more sophisticated zombies or as a type of humanoid monster that eats humans.
In SLASH'EM, ghouls have been made slightly more dangerous, paralyzing for 1d6 turns and doing 1d4 damage, as well as having a base level of 5. A ghoul is also the starting pet for a necromancer.
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