Closest I come is one where Starlight's time meddling made him an abusive jerk and her a doormat.

Zero so far. I haven't read too many fanfics with Sunburst in them at all, though.

I've checked out Sunburst fanfics but even I haven't seen a villainous streak yet.

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wow, so having planned to put Sunburst (possessed) as the final boss of my fanfic, it wasn't a bad idea, hahaha

I'm still writing it, I hope no one copies my idea.

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As long as you take the time to really develop his character and villain arc, you should be fine!