[Horrified]

Adding some online elements to it would be the main factor, and the fun factor. There's no way I'll play a Graal version of Mario, I'll go ahead and play Mario. There should be something different that makes it interesting.

For example, maybe the NPCs that the players kill can be controlled by other players, or something that would make things more interesting and challenging for both players. Also, having a 2-D Side scroller like Mario would suck having 10-15 players on a screen at once running to the right.