I can do one better, in a campaign I was in a few years back it turned out that due to some time travel shenanigans and an attempt to find a loophole in some wish-induced immortality, my character literally was one of the Big Bads. I went back in time, killed her before she became immortal, and impersonated her for 1500 years. To maintain the integrity of the timeline I had to do all the stuff the Big Bad had already done up to the present day, but as soon as the clock struck “Now” I (as that Big Bad) flipped sides to join the party.

I brought an army of minions and plenty of intel about the other Big Bads along, too. Quite a fun bit of plot judo.

At least one timetravel nerd just got an aneurysm about how that would break all sorts of things

Have you considered: Magic

Awesome!

The best part is that that particular Big Bad was responsible for my character’s origin, so my character became quite the Ouroboros out of that. She was epitome of a self-made person.

I know where I came from—but where did all you zombies come from?

This is The Witcher’s Ciri if you substitute Dragon for mental powers she can barely control, which is kind of like a dragon. And she does switch up her skills for the appropriate times.

You are an old Buffy fan.