I suggest you make a good physics engine first. Don't even bother to make sprites. It can be easy to spend all your time making sprites and realize when you are done that you can't make the game. Black rectangles will do at first. Even if the graphics are perfect, the physics needs to feel at least somewhat realistic. I might even go so far as to get some video of Smash for analysis. (Any youtube video will work). How high do the characters jump? 2x their height? Having a video to base it off of helps. There is a version of Smash for the ti-83+ written in Axe.