Eris

Eris is a Greek goddess.
She's the goddess of strife, discord, and chaos.
[link]

I just felt like drawing her as a pony...
and because she was a goddess, I thought of making her an alicorn... but nah.

her cutie mark is the golden apple of discord
don't ask me WHAT kinda trouble she had to make to get that

I'd say that she'd be one to creep around, secretly causing chaos. The mischievous type.

But I think even she'd have a good side...
She might not cause physical harm and help (a bit) if you're actually hurt.
She would apologize if her trouble making got out of hand (maybe)