One Piece Episode 612

[DarthEnderX]

I suppose the other possibility is that she has two fruit powers. Maybe she's a prototype.

I think if she was actually a zoan, we'd see her shifting occasionally. She hasn't changed from "hybrid" form for the entire arc and only appears human in flashbacks.

It's not overly likely somebody like Blackbeard came up with the technique by himself.

It's because he ate the Chimera Fruit.