This game is stuffed to the gills, but I'm already imagining DLC:
- Koopalings: Shake them to change their attack style, with several variants each.
- Slopes: Set two points, and the game connects them. Allows for variable steepness.
- Rotating terrain: clock gears, ground wheels, platforms you can spin, etc.
- Crushers: Falling ceilings, rising floors, walls that move in and out, spike pillars, etc.
- More level types: Desert, beach, forest, ice, mountains, clouds, etc.
- More enemies: The dinosaurs of Super Mario World, etc.
- Maybe a new style: SMB2, with unique mechanics?