firefrorefiddle is the name of a character from the popular musical "cats" who is said to be created and played by gus the theatre cat in the movie he appears as a ghostly figure I suggest you watch it but pay attention the second act when gus is singing you'll know its the right number if they mention "firefrorefiddle the fiend of the fell" repeatedly.

I pretty sure it's Gus!

Next to the theatre tower

The prologue, (although she is not yet decked out in her full Gumby cat costume), The naming of cats, Jennyanydots: The Gumby cat (obviously), The Rum Tum Tugger song, Grizabella: the glamour cat, Bustopher Jones, Old Deuteronomy, a little bit in the Aweful Battle of the Pekes and the Pollicles, The Jellicle Ball, The Moments of Happiness, Gus: the Theatre cat, Skimbleshanks: the Railway cat, the Macavity battle sequence, The Magical Mister Mistoffolees, Memory reprise, The ad-dressing of cats.