As a free to play player, my options are limited which means no overheal and minion heroes so had to get creative. and it is indeed possible! I did get very careless near the end and lost a bunch of heroes so definitely pay attention to the end.
This is the same team I used for the last 5 levels. Vivica and Kadelien are important as they make counter attack viable by reducing the incoming damage to tolerable and recoverable levels.
For skills, I focused on healing (+25%), minions and 30% mana regeneration to keep counter attack up as long as possible.
The tornadoes/hurricanes are mostly as a survival technique - especially in the mob stage where I could easily lose my 4* heroes if Iām not being careful.