The mechanics are really interesting; because the actions you take with the buttons still activate, there's all kinds of interactions, like missing platforms because you're holding sprint and you're suddenly faster than you anticipated.
I had a bit of an issue with pressing all the buttons with others pressed, though I often have this problem with games; e.g. (on a controller) holding B while pressing A is just a bit tricky. The shoulder buttons would have been useful here, perhaps? (Don't know what to do with the keyboard controls though!)
Anyway, cute game with an interesting core mechanic. Nice job!