Very cool and satisfying concept! I definitely could see this going in some interesting directions if continued. Like the mana didn't really matter because I ended up with over a million at the end anyway, that could be more limited creating some strategy. Maybe it could be a highscore game where you have to destroy as much as possible before running out of mana. Maybe it could be a strategy game with different levels being different cities that each progressively get harder to fully destroy. Whatever you do, this is pretty cool already!