The body base for this figure is a Batman Forever Two-Face.  The head is from an animated Mr. Freeze.  The hat is from a Shadow figure and the cape is from a Detective Batman.

I trimmed the gun in the left hand down to a "gas gun" that the Gray Ghost might have used.

I used plumber's putty to make the front part of the Ghost's tunic and the attached buttons.  I also trimmed the lower portion of the original suit coat to fit in line with the Ghost's tunic.