Assuming that you're not gonna go the route where you add unique music to this amazing game of yours, might I add that some Legend of Bumbo tracks hit hard?
Also, what if, putting a new Cube of Meat onto an already placed (undamaged) Cube of Meat upgrades them like in the original game? Maybe to balance it out, doing so will cause the Cube of Meat card to become more expensive and have longer cooldowns for the rest of the room? Upgrading a single Cube of Meat to level 2 will make the card more expensive. Leveling up any Cube of Meat to level 3 will make the card more expensive for the rest of the room and so on and so forth. When you upgrade a Cube of Meat, the card does not spawn upgraded Cubes of Meat when used afterward, just a normal level 1 Cube of Meat. Maybe it can be an upgrade unlock? Like... you can't upgrade them until you get 'this specific' achievement for example?