View Bosses:
Select two player mode. Press L + R on controllers one and two at the character selection screen. The final Bosses of the game will appear in the lower right corner of the screen in the place of the question marks.
Use rescued characters in 1 Player Vs. mode
After having defeated a character, but before the next battle begins, you'll see the main character running accross a rainbow. This is when you input the code. Hold "X" and "Y" and press Start A "character select" box will come up, allowing you to swich characters before the next fight.
Use Rivals/Bosses During Multiplayer
Go to the "Player Select" Screen Hold the L and R buttons on both player 1 and 2's controllers for 3 seconds. The bosses will appear and can be used in combat now.
