FWP said: "Regular Body Ghost" have enough mass for that to be a problem?
In Gensokyo, there are three kinds of entities generally confused with each other: ghosts, phantoms, and poltergeists. Yuyuko is a ghost while Youmu is a half-phantom, for example.
Phantoms are completely intangible and formless - those blobs that float all around the Netherworld, for example, and what we call Myon. They can arise from a body, living or dead, and many phantoms may form from a single body. (They are based on what spurned them, so Youmu's ghost half is considered a separate entity and Youmu at the same time.)
Ghosts, exclusively formed from dead humans, have specific forms and bodies that are corporeal enough to make passing through solid substance, as a phantom would, not simple. This also allows them to touch and feel things and possess "mass."
A poltergeist has properties similar to a ghost or a phantom, depending on the poltergeist. The main difference is that they are artificial creations.