This legendary special, believed to be forever lost until recently, featured probably the strangest cast of any network special that I've ever seen. From Wikepedia;
"The Paul Lynde Halloween Special was a Halloween-themed television special starring Paul Lynde whose first (and only) broadcast was October 29, 1976 on ABC. It featured guest stars Margaret Hamilton as The Wicked Witch of the West from The Wizard of Oz, Billie Hayes as Witchiepoo from H.R. Pufnstuf, Tim Conway from The Carol Burnett Show, Roz Kelly from Happy Days, Florence Henderson from The Brady Bunch, rock band KISS, Billy Barty, Betty White and (in an unbilled surprise appearance) Donny Osmond and Marie Osmond."
I've never seen the whole special, but I have a friend who bought the DVD and says it's the trippiest thing he's ever seen; pure 70's gold!