Pointless game. All it does is force you to grind to level 9, upgrade the purple summon to 100% chance. Then you win the game once you get 6 purple summons. Every single level can be beat with 6 level 1 purple summons. The bursting stars are just overkill.
The alien side is basically easy mode. There is a flamethrower type unit for land, air, and sea. All you need is the invisibility skill upgrade, and you can just monospam that flamethrower unit to win.