The Ghost was designed to be a straight flying disc capable of pin-point accuracy from the fairway as well as significant distance off the tee pad. Faster than traditional mid-ranges, with greater glide, the Ghost maintains a nice fade at the end of its flight path.
Gravity Edition is definitely a softer, more flexible plastic for Legacy Discs. Many putters out there truly appreciate the softer feel, leading to more confidence out of the hand and into the chains. This plastic also tends to be slightly less stable than the stiffer Protégé Edition plastic supporting a softer touch around the chains.