The Fleeing Ghost looks like a typical ghost with one red eye in the middle of their forehead. Their lips are puckered up, giving them a silly expression similar to someone pretending to be innocent after a misdeed. They can be found in The Ghost World and the Triangle Kerchief Effect can be obtained by interacting with them.
They move quite fast and flee from Madotsuki which is the inspiration for their fan-given name. The easiest way to catch them would be with either the Stoplight or the Cat Effect, as they show a normal reaction to both effects. They also react normally to the Knife Effect like most NPCs.