The normal wobble effect when flying got increased by a ton, so the entire ghost as a whole ends up oscillating wildly. Not sure if it’s a Mystic Grove exclusive thing, haven’t been able to play any other map.
I think it happens on every map:
I believe this is a side-effect of the effect they use for the displacement on all ghostly materials (ZM Ghost, Halloween Jetpack, etc). A similar thing can be seen when crouching with the Halloween Jetpack (the wobble effect will move based on which part of the model is lowest).
I believe the displacement of the shader is determined globally (as opposed to being related to the object’s UV map or topology) and will react weirdly as the object moves.