Canonicity in all its glory.

well, I don't know... I think it should be something like this:
Assassin (invisibility, strike-return, poison, counterattack)
Hunter (ranged attack)
Twilight Witch (healing, melee combat) / Beholder (healing, ranged attack)
Minotaur (similar to the one in Heroes of Might and Magic V, but with slightly weaker stats)
Manticore (poison (basic), paralysis (upgrade), melee combat, counterattack) / Hydra (poison (basic), paralysis (upgrade), melee combat, counterattack, regeneration)
Faceless One (berserk (basic), mind control (upgrade), strike and return, counterattack)
Black Dragon (dragon breath, resistance to darkness, 50% immunity to all other magic)