I tried to make a game where you control the rotation of the main character's two stick legs, but the end result was crashing. So I changed it to hopping and alternating feet.
Shift will make you move slower horizontally. Don't let your rocket arms bump into anything. Your feet check constantly for active object overlap, so sometimes it's possible to run across stretches of thin or tiny blocks.
I, uh, need to find a replacement for K&P that doesn't crash. I'm very familiar with the K&P/MMF system and maybe this has been holding me back from switching? I'll look into Game Maker.