It increases the size and strength of the player. (Turns Normal X into Super X)
It gives the player their unique powers. (Turns X Mario into Fire Mario, X Luigi into Ice Luigi, X Renegoomba into Hammer Renegoomba and X Boo into Boomerang Boo.)
Turns the player into a temporary "mega" form.
Turns the player back a stage. (Mega turns into Intense Fire/Ice/Hammer/Boomerang, Intense Fire/Ice/Hammer/Boomerang turns into Fire/Ice/Hammer/Boomerang, Fire/Ice/Hammer/Boomerang turns into Super, Super turns into Normal, Normal turns into Mini.
Intensifies the player's unique power.
If the player is Mario or Luigi, this power-up will give them both blue shells on their backs. They can slide, but not just that, they also become immune to Mini Mushrooms. If the player is not Mario or Luigi, this will serve as a normal enemy shell.
Gives the player invincibilty for a short amount of time.