Rich Little plays 18 different characters: W.C. Fields as Scrooge, Paul Lynde as Bob Cratchit, Humphrey Bogart as The Ghost of Christmas Past, Peter Falk as The Ghost of Christmas Present, Peter Sellers (playing Inspector Clouseau) as The Ghost of Christmas Yet to Come, Richard Nixon as Jacob Marley, Truman Capote as Tiny Tim, Groucho Marx as Fezziwig, Jean Stapleton (playing Edith Bunker) as Mrs. Cratchit, Johnny Carson as Fred, James Stewart as Dick Wilkins, John Wayne as the 1st Businessman, George Burns as the 2nd Businessman, James Mason as the 3rd Businessman, Jack Benny as the boy at Scrooge's window, Stan Laurel as Mr. Laurel, Oliver Hardy as Mr. Hardy, Dean Martin as the new partner.
That was real buttermilk that Little drank at the end. His reaction was real.
All three of the spirits are famous detectives - Humphrey Bogart as Sam Spade, Peter Falk as Columbo, and Peter Sellers as Inspector Clouseau.
The scene near the end when Clouseau sets the curtains on fire was not done on purpose. When the curtains started to burn, Little got the idea to keep talking until the fire became a problem.
The set in which Scrooge is talking to the young boy was a scaffold. He was told not to move around too must lest he fall to his death.