User with this ability either is or can transform into a spirit: a supernatural and conscious (although not necessarily sentient) being that in its normal state is incorporeal, invisible and immaterial. Many spirits are able to materialize either by shifting into a more solid form or by taking a vessel to give them physical shape, which can be done either by possessing an already existing form (either a living being or an object) or by animating and wrapping part of the environment "around" them.