Diablo (3.5e Sourcebook)/Monsters

Monsters
Balrog (As imp or balor, MM1)

Fallen One (Half-fiend elf sorcerer, MM1)

Gargoyle (MM1)

Goatfolk (MM3)

Horned Devil (MM1)

Knight (Bone human knight, see BVD and PH2)

Lightning Demon (As quasit or pit fiend, MM1, but deals electricity damage rather than fire)

Mage (Bone human sorcerer, see BVD)

Magma Demon (Fiendish magma paraelemental, MM1 and Manual of the Planes)

Overlord (Bone human wizard (enchanter), see BVD)

Scavenger (Fiendish wolf (or dire wolf) skeleton, MM1)

Skeleton (MM1)

Succubus (MM1)

The Hidden (As invisible stalker, MM1)

Viper (MM1)

Winged Demon (As erinyes, MM1)

Zombie (As corpse creature, for any humanoid with class levels, BVD)

Bosses
Diablo is a pit fiend with enough levels of necromancer (but with the Diablo domain) to make him an appropriate challenge for the PC's.

King Leoric is a bone (see BVD) human with enough levels of necromancer to make him an appropriate challenge for the PC's.

The Butcher is a half-giant (see EPH) with enough levels of barbarian to make him an appropriate challenge for the PC's.