Use space/up arrow/click to move up and release to go down. Press "Z" to do weird things. (Become a mini wave.) Don't forget rule one, though: DON'T DIE. Blue is easiest. Green is medium. Red is evil.
RobTop Games gets credit for death sound and for popularizing the wave concept. Thanks to @Cv1f for helping fix a glitch caused by Scratch 3.0.