The most useful monster.

In my opinion, bone dragons are better than devils. 1) Dragons have more melee defense and even more ranged defense. 2) They have more speed. 3) The aura of fear + the first strike = no retaliation. Moreover, the remaining creatures will no longer be able to attack the bone dragons (or almost not), the dragons will attack first again and inflict fear. 4) Dragons look better than demons.