Dissociative Identity Disorder (3.5e Trait)
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 Dissociative Identity Disorder
Dissociative Identity Disorder is a case where the subject has two or more different personalities, with no memory of the actions of other Alter Egos. This cannot be caused by drug use or other general medication.
Benefit: You essentially have two characters inhabiting one body. Both Alter Egos share physical stats (Strength, Dexterity, and Constitution) but have separate Mental Stats (Intelligence, Wisdom, and Charisma). Personalities also share different traits, such as ranks in certain skills (DM's Discretion), and certain feats (Dm's Discretion). Only one personality may be in use at any given time.
Drawback: These Alter Egos cannot be selected to appear or disappear. They usually manifest in response to a certain stimulus. For example, a Wizard being menaced by a Dragon might also have a hidden Barbarian Alter Ego that appears under serious stress. Likewise, a normally quiet, simple Commoner might find himself entirely naked next to a gorgeous Aristocrat after a night of wild Bardic partying.
Normal: Characters have a single, set personality, and one character design.
Roleplaying Ideas: Characters with this trait are often very unpredictable, as you never know which side you'll be talking to. At one point you may be discussing contemporary theater with a renown Bard, and the next you may be arm-wrestling a brazen Fighter.