This really isn't a cheat but i'll tell you what all the disguises do(in order from when you get them):

Thief Wario: Touch the screen and he rams into your enemy. He also jumps the highest.
Cosmic Wario: Touch the screen and he shoots a laser. Get the mastery gem and the lasers bounce off of the wall. When he jumps he sort-of hovers in the air. Arty Wario: Use the stylus to draw a Block, Door (back to the last saving point or if you haven't saved to the begining of the level), and a Heart (if you get the mastery gem). He can't move though.
Genius Wario: He can see hidden things like doors or holes in walls. Get the mastery gem and touch the screen to punch.
Sparky Wario: He lights up a dark room and if you touch the screen he lights it up even more for a short while. Get the mastery gem to shoot little sparks at your enemies (when you touch the screen).
Captain Wario: He is useless unless your near water (or lava in Sweatmore Peak). He can swim on water and swim against the current. Get the mastery gem to go under water and shoot torpedos.
Dragon Wario: Touch the screen to breathe fire and destroy fire blocks. Get the mastery gem to breathe blue fire and destroy water blocks. He can also fall through thin platforms and he jumps the lowest.
Wicked Wario: He can fly if you blow into the microphone. Get the mastery gem to fly left and right instead of just up and down. He dosen't attack but if you fall he falls very slowly.

Hope it helps!!!