EX Characters

Unlocking EX versions of the characters (basically the same character with a different move set) can be done through survival mode. Every twenty levels you'll face the EX Shadow version of a certain character, and defeating them unlocks it for your own use.

Gold/Shadow Characters

Like EX characters, they can be unlocked through survival mode. Once you've gotten to a high enough level in survival, you'll start facing the gold forms of each character (every twenty levels). Defeat them to unlock them for your own use. The other way to unlock them, is via time release.

To select a Shadow character, press Zr (Classic Controller. Whatever button you use to change the color scheme) until reload appears below the character. Then press Dust. To select a gold character, press Zr until Slash appears below the character, and once again, press Dust.