The following categories of monsters are sometimes referred to in the rules.

Magically created or animated monsters (including undead), and those summoned by spells or magic items.

The following monsters are classified as persons: Acolyte, Bandit, Berserker, Brigand, Buccaneer, Bugbear, Devotee, Dryad, Dwarf, Elf, Gnoll, Gnome, Goblin, Halfling, Hobgoblin, Kobold, Lizardfolk, Medium, Merchant, Merfolk, neanderthal, Nixie, Noble, Nomad, Normal Human, Ogre, Orc, Pirate, Pixie, Sprite, Trader, Troglodyte, Veteran.

Monsters that were once alive but which have been dragged back from death by evil magic. Undead are immune to biological effects (e.g. poison) and to mind-reading or mind-affecting magic (e.g. ESP, charm, hold, sleep).