Here Arthur Rankin Jr. and Jules Bass pool talents with Joseph E. Levine, Harvey Kurtzman, Len Korobkin and, on microphones, Boris Karloff, Phyllis Diller, Gale Garnett and Allen Swift. The plot revolves around Dr. Frankenstein's decision to retire and leave his work and island to his nephew. The Mad Monster Party brings those two together as well as Frankenstein, the Bride of Frankenstein (called "Monster's Mate" here), the Invisible Man, Dracula, the Wolf Man, The Mummy and more. And things take a menacing turn when Dr. Frankenstein's assistant Francesca makes a deal with Dracula to team up and take the nephew out so that they will have all Dr. Frankenstein's secrets to themselves.
What you'll mainly learn is how messed up Rankin and Bass were.
Francesca ends up following in love with Felix, Dr. Frankenstein's nephew. How? While plotting to kill him, she explodes verbally at him and he slaps her. "Oh, Felix!" she coos. He slaps her again and she's soon singing "Never Was A Torch Like Mine" ("for you"). Or earlier, when Dracula and Frankenstein get into a fight and Francesca and the Monster's Mate are fighting, the women pull off each other's clothes (the men don't) and you hear the hissing and snarls of cats as the women fight (not when the men do).
It's a very curious artifact and it's streaming online now at Netflix (Netflix membership required to view).