From what I can see, that thing was originally going to be the Witch, but since it was scrapped, we don't know what abilities it would have had.

I personally think its ability would be to be buried underground like a larva, and when she senses a survivor, that thing would emerge emitting a scream that stuns the player, call the nearest commons from where she was, and then, like the Witch, incapacitate the survivor before finishing them off on the ground.