I think your game sounds fun! In particular I think the idea of being able to play each card either as defense or offense sounds really unique, and strategically interesting (if I have a +3, do I want to use it to make sure I don't get killed by that enemy, or use it to take out this other enemy?). I think your theming is really cute, especially having the enemies be different forms of litter. I would say, though, that your scope seems a little wide, at least to my ears. Having 4 types of enemies, other types of hazard, and treasure chests sounds like a lot, not to mention that you also want to have 5 full levels and a boss fight at the end. Maybe you'll be able to get it done in the time, but it never hurts to have a plan for what to cut.