Tactics Treatise - raise morale?

[BB Shockwave]

You can resurrect those losses later. I hope you have invested in the Concentration skill that lets you recover +2 to +6 mana per round? It's a lifesaver here. Or, use the spell Magic Spring. Try to kill those towers, no matter their retaliations - I usually manage to kill one in the first round before it could act, and 1 every other round.

Sheep is a deadly spell, but these Gremlins can only cast it on level 1-2 units. So either do not bring those, or use Dispel.