Oh, this is ridiculous. She isn't about to get run out of a swamp by this guy, but they're also still technically working together, so leaving him dead in the mud isn't an appealing option. That and it'd be a little overkill for frightened showboating, to off a mage over that.

"Keh," Billie's shrill rat noises trail off with a displeased sound and then... she vanishes. The air around her seems to twist for a second, then she's gone. It's exactly the same way her teleportation while as human worked if Strange happened to be paying attention.

It puts her right behind him, bones cracking and shape changing as she steps out of one spell and releases her hold on, well, not quite a spell. She imagines a shiftling's talent is a magic of a sort, though the change is instinctive, not something calling for a magic word or learned from a book. It just is. Anyway, it'll be as a human Billie that she makes a grab for his pointy ear, to yank it and his head down if she gets it.

"What in the abyss do you think you're doing, just harassing anyone you stumble across?!"