What made Cozy Glow evil?

That was the question that everypony would wonder whenever that peculiar name would be heard. Was it her cutie mark? Was it her parents? Was it both? Or was it something more?

A few nights before Twilight's coronation, the Princess of Friendship ponders those exact questions.

Then, there was a knock on her castle doors.

Note: Just a random idea I had. Just a heads up though, this is NOT canon with The Dawn of a New Mission, or ANY of its sequels, present or upcoming. This is a standalone fic, and NOTHING more!