@Greengiant302 make sure you have the spell vanquish and make sure you have the fire cloak
you then need to cast vanquish to kill the support minions which leaves the demon horde leader vulnerable.
good luck ;)
one thing that ruins the game for me is the missile things because of them always having to land on the short buildings so i have to jump over them and then fall into the abyss
im only on the third mission with the tanks and its impossible because there are tanks coming nonstop and my bazooka team can never actually hit the tank wich makes this game fail