From Diablo Wiki
Monster Types is one of the four classifications of monsters in Diablo III. All monsters belong to one of the classifications in Diablo III, and certain spells or items are more effective against different types of monsters. This article also contains the lore information about Monster Types.
The classifications of monsters in Diablo III are:
- Beasts (category) - Feral, unintelligent enemies.
- Demons (category) - Mostly sinister, sentient monsters from Hell.
- Humans (category) - Corrupted and hostile humans.
- Objects (category) - Stationary obstacles, like traps.
- Undead (category) - Varying types of re-animated corpses, mostly from humans.
- Reapers (category) - Corrupted Angels and Malthael's constructs including undead.