Once you have defeated Ansem between Floor 12 and Floor 11, you can use Riku's darkness/Dark Mode. You can activate Riku's darkness/Dark Mode by withstaining damage from enemies or by breaking your enemies' cards. Every time you get hurt you gain 1 Dark Point and when you break an enemie's card, the difference between your card and their card is how many point you gain (If you use a 0 card, you gain Dark Points equal to the value of their card. If you use a sleight to break a card, the max amount of Dark Points you can recieve from the break is 9.) When you reach 30 Dark Points, you transform into Dark Mode. In Dark Mode: your attacks are stronger, you are slightly slower, you can use sleights (the sleights are Dark Break: Soul Eater total 5-15, Dark Firaga: Soul Eater total 16-25, Dark Aura: Soul Eater total 27), your attack combo is different, you can jump and jump again in midair and land behind an enemy, right before you land behind an enemy you can attack to jump up and attack your enemy's back. When in Dark Mode every time you get hit, you lose Dark Points equal to the value of the enemy's card and everty time your card is broken you lose Dark Points equal to the distance between your opponent's card and yours (If your opponent uses a 0 card to break your card, you will lose Dark Points equal to the value of your acrd that was broken. If your card is broken with a sleight, the max Dark Points you can lose is 9.) When your Dark Points reach 0, you will return to normal.
AP is Attack Points. The higher your AP is, the stronger your attacks are.
DP is Dark Points. When you transform into Dark Mode, your DP will automatically set to your Dark Point amount. The higher your DP, the longer you can stay in Dark Mode.