Board Thread:Character Discussion/@comment-25926288-20170502151008/@comment-25375217-20170503150639

What about...

Fiona (Ursula): She went dark after she was stopped from trying to do the right thing.

It's a stretch since Fiona's "right thing" was casting the Dark Curse while Ursula's was sparing humans from violent death by shipwreck... but y'know.