Phantasm
The Phantasm is the titular character from the 1994 animated Batman movie, "Mask of the Phantasm". Now stop reading this and go watch the movie. It's one of the best Batman movies ever made, and it's probably been a while since you've watched it.
So go - watch and enjoy "Mask of the Phantasm" right now - it'll explain Phantasm better than I will. I'll still be here when you come back.