Character forms are different forms that a character can take. They may differ in appearance, personality, stats, or moves. Uber Forms are an example of this, because they are upgraded versions of the character's orignal form.
Characters can change into a certain form when being in a state where that character would usually be in a fainted state, or they may require other conditions to be activated.
For a list of characters with multiple forms, see Category:Aquablade Chronicles Characters with multiple forms.