Not super happy with my idea but couldn't think of anything better (except for battle royale Tetris puzzle in space with floating islands crumbling apart). So here is what I come up with; an old-school fps with a couple of enemies who only have melee attacks. Levels are tile based. Some of the tiles are destructible and some are not. You cannot kill enemies, only stun them. The purpose is to collect some parts from tiles to repair the portal in the middle of the level. The catch is every time you stun an enemy a new tile spawns. Every time you destroy a tile two other tile spawns. So if you are trigger-happy or not careful, you will run out of space very fast.