Nice game; fun, well made, and with a lot of polish! Love the low-res art style of the game. Also, nice way of incorporating the theme, really creative! (Also, love the difficulty!)
One thing I'd suggest though; consider adding "c" in addition to "z" for jumping, as it would allow the player an easy way of choosing which finger (middle/index) to assign to which action (jump/zap).
Other than that, great job!