There are many ways to balance Factions, and it's not necessary to give creatures special abilities. For example, Angels had resurrection, which made them unique. And Devils had teleportation, which was a unique ability (as far as I remember, it was the only unit with this ability). And teleportation is not just simple movement; it's needed to overcome obstacles, quickly block/disable archers/casters. Therefore, I think it's better to give Devils a normal teleportation ability, and the developers can balance the Devil with other units.
Moderated: OFF-TOPIC in the message
Цикл "Закадычные враги": "Особенное гостеприимство, "Супероружие", "Меж молотом и наковальней"
"Падение Шантири"
Кампания для "Кодекса Войны"
"Выбор Сагиттеля"