Super Plasma Bolt:
Hold the UP arrow for about 2 seconds until you hear the "charge up" noise. Then press the Fire key. You'll take a hitpoint of damage by doing this.

Fireballs:
Turn left and right in succession about 6 or 7 times and press the Fire key. You'll take a hitpoint of damage by doing this.

Shield:
Turn left and right in succession about 6 or 7 times and press the Jump key. You'll turn a different color, and a shield will appear around you. This lasts a very short amount of time.

Invincibility:
Hold the Up arrow at least 2 seconds, then press the Down arrow. You will flash and be invincible for a very short amount of time.

Thanks to Revolution reader Rohan Joshi!