Full Pause Screen.

At the Pause Screen, Press X + Y.

Maximize Your Levels.

Start the game in the first level in the Mountain World. Stand in front of the first set of stairs and keep firing. Unlimited green trolls will continuously come at you. Continue to fire until you have maximized your levels to where you want them. Using a controller with an auto-fire feature is very helpful with this trick.

Bonus Characters.

Get to level 25 with each of the four original characters. Now load the character and create a new one through the managment option. Hold Turbo down and they will now turn into their counterpart.