I thought this was a cool and original idea - I especially liked the "boss" level: swapping between the arm and leg modes while on a timer was a lot of fun! Great job, and this definitely feels like it could be built out into something really cool.
There was one small bug I encountered on the last level - I think I jumped over the boss spawn point and was confused as to why there was nothing in the level, but I eventually figured out what was going on and was able to fight the boss.