This translucent, silvery crystal is related to phase rock (see Manual of the Planes). It can be induced to discharge its extradimensional energy and shunt a creature out of phase for a short time.
Effect: When a creature ends its move in a square of phase crystal, it gains phasing until the end of its next turn. That square cannot affect another creature until the end of the encounter.
Usage: Combined with obstacles that restrict a battlefield, phase crystal allows characters or monsters greater mobility. You can restrict the terrain’s effect by limiting the number of squares it covers. Try not to use phase crystal as the only way to get to a special area or encounter unless the terrain is large enough to affect the entire party at one time.
Published in The Plane Below, page(s) 17.