for the final boss: don't make any ranged units! no archers, catapults, cannons, wizards. play elf and when the boss comes spam forest guardians (to hurt the boss) and one or two angels (to kill the other random crap that comes up behind the boss). he won't even move. way easier than "the end."
the game has nice graphics and interface but is way too easy. especially when you build a custom deck and can load it up with whatever overpowered units you want. and the AI isn't great.