So I had a dream about my ponysona again. He's an alicorn, and this time, he ended up transforming himself into a Nightmare.

No, that's not Nightmare Moon possessing him. He had other ponies chasing him and trying to catch him and control him, and his refusal, his definace, was SO strong, that he transformed into a Nightmare. (Nightcolt? W/E who cares)

Nightmare Defiancy (or Defy) is not necessarily evil, but instead, will bring out a pony's stubbornness, and any rebellious nature that they may hold. Depending on the pony the new entity is controlling, they can be either evil, or chaotic good.

PLEASE NOTE: Before you decide to go "THAT'S SO OVERPOWERED WAH GARY STU!!", these events have been happening in my dreams, and I would have otherwise never come up with them OR drawn them. Also, I don't roleplay, so there's no problems there. (I still think my dreams come up with better OCs than some people do.)