Neat idea and has everything a retro platformer needs. The keys and the small margin for error made it unplayable for me. I'd want to change the action button 'stone legs' to space button and when having to hit a certain spot when jumping, it's just too small to see where I have to land even though my screen is 22 inches. Maybe the gap could be widened by 1 or 2 pixels or you could choose the speed of the game.
Thanks for sharing it.