Hot Barrel Cats

A defense game that runs on overheating. Cats on the wall shoot the fungus horde marching toward your gate, and every shot heats the cat that fired it until it jams and has to cool off. So the game is not about firepower, it is about rotation: drag the hot ones down to the spawn zone, send fresh ones up, and keep a line firing at all times. Two matching cats dropped together merge into a stronger tier and come back completely cool, which makes merging a defensive move as much as an upgrade.