So I know a lot of people like to depict Mane-iac as the pony equivalent of the joker, but I was wondering what do you all think of a character that only comes across as insane when she is acting out the role of the villain but for the most part acts and seems fairly normal (aside from the seemingly sentient mane) in her normal life?

Also what would be a good way to explain such a change?

As her back story is similar to the Joker (falling into a vat of chemicals) it might possibly be the result of a chemical imbalance. She has gone 'evil' mentally, but the physical effects (madness) could be initiated by brain 'endorphins (?)' created when she gets excited or naturally high reacting with brain damage or residual elements from her accidental dip in the vat.
Calm and cool = normal reactions
Excited or 'UP' = maniacal reactions

I am not Humdrum nor am I humdrum.

7194609 That's an interesting thought.