I really liked the Dungeon Lords, the Rakshasa Rajahs, and, of course, the Twilight Witches (I play as Dungeon).
But I think the Paladins were better in the third game. And the Undead are just okay; the Death Knights were much cooler:(
According to the rating, the Ancient Ents are far behind:( But they have a lot of hit points! They often saved me in difficult situations.
Ancient Ents are the best, thanks to their HP; they often saved me. It's a pity that they have low initiative. Rakshasa Rajahs and Shadow
