Oh that kind-hearted Rose, always taking in strays.

Greg and Lion are real big mysteries in the show, though. Lion, obviously, because nobody knows what he/she is or why he/she has Rose's stuff. Greg's a mystery because of his talk with Steven in the van before the final fight, he acted really suspicious. Like he might be involved with something bigger than just being a human Rose happened to fall in love with.

And if you ask me, Rose (or anyone) wouldn't want to be with Greg for no reason.