yuriy, try the Demon skill combined with Leadership and Luck – you won't regret it. In version 3.0, with this build, my Agrael in the 5th mission of the original campaign cleared all the dungeons and, in the end, defeated 72 dragons without losing a single unit. Summoning is not needed. It's just that Leadership is difficult to obtain. But I was lucky – I got it quite quickly. With the speed aura, the dogs and unicorns immediately reach the druids.

IMHO, leveling up a mage's skills on a map without a mentor in a game against a human player is a guaranteed loss.