For now my strategy rely upon a lot on upgraded archers and some kind of tanks in front. It’s very random : if I can obtain a gold upgrade on some units, and apply a second gold updgrade, I can progress, if not I cannot go very far. So for me it’s very luck based and quite frustrating. But I have fun ! I tried the cleric and the fire wizard with no success, and the alternative to the archer also did not work (I forgot his name).
So I don’t know, maybe I’m just not good enough 😂