You must use the very bottom path for every match (easiest) on adventure. When you get to the end, you will have a match with 3 other Digimon in the Ice Palace. When you win you will automaticly unlcok the Ice Palace for other game modes!
Evolve energy item
At the title screen press TRIANGLE, RIGHT, DOWN, CIRCLE, L1, X, R1, X, TRIANGLE.
Evolve meter always full
At the title screen press SQAURE, RIGHT, X, TRIANGLE, LEFT, CIRCLE, L1 + R1.
One-hit Dead Rule
At the title screen press RIGHT, UP, LEFT, DOWN, X, L1+R1.
Unlocking Black Digimon
To unlock Black Digimon (Black Agumon, Guilmon and Gabumon) you must defeat them in Adventure mode. You will find them as random encounters and they are harder then other Digimon you have to fight. When you win, you will unlock that Digimon for all game modes!
Unlocking Boss Digimon
To unlock boss Digimon (MaloMyotismon, Duskmon, Omnimon, Diaboromon, Neemon) you must defeat them in a battle. When you win, you will unlock that boss that you have defeated for other game modes. As an added bonus, you will also unlock the arena you fight the bosses in for other game modes too (you only need to beat one boss to unlock the stage)!
Bonus Stage: Ice Palace...