Character with a split personality

[Psysama]

Okay, I have done this time and again in a lot of my campaigns:
A cute innocent girl with a psychotic dark side.

I've had my friends I game with even help me with making some of them.  This time I want to see ideas; what would you do? How would you do it?  Give me feats, traits, flaws, classes, etc be they official content, third party content, or homebrew.  I want to see YOUR ideas (its always good to look at a new perspective).

Also, I am looking to create something that allows the PCs and NPCs to VISIBLY see the change in personality.  A flaw or a trait or something.  Let's see what you got!

(click to show/hide)

Examples are (but not limited to)(Cause of change):
Dr. Jekyll/Mr. Hyde (a special potion)
Launch (from Dragonball) (when she sneezes)
Ryu (Street Fighter)(His desire to win?  I didn't play Street Fighter much sorry.)
Pinkie Pie/Pinkamena (My Little Pony)(When she is feeling insecure believing she is not needed or wanted)

[bhu]

Maybe a combo feat/flaw that are paired together?  Have the flaw be the multiple personality disorder and the feat maybe some minor bonus thats dependent on which personality is in charge?

And of course theres always Frenzied Berserker   

[Mr. woop woop]

If pathfinder is aloud, there is a alchemist prc that has split personalities.

Personally, I think she should have a different set of certain stats.
•str: Mabey in her sycosis she can't hold her strength back. Every attack can deal more damage (*3 str?) but causes X amount of hp damage
•dex: in the blood thirsty frenzy you become less nimble -x to dex
•con: no change(a secon mind can't cause your body to withstand more harm) or Mabey you can continue fighting until your hp =-con modifier (like someone in crack?)
•Wis: (you can't get more wise... I think)
•int: (you can't get smarter) Mabey a refill on knowledge checks to represent that while knowledge is based off what you know, the split personality might know more.
•cha: better or worse for being crazy?

[Arz]

Use tattoos of mind seed and psychic reformation. BAM!