"Mad Monster Party?" was produced by Arthur Rankin and Jules Bass and released in 1967. This is a nostalgic childhood favorite of mine, as it would air on TV around Halloween back in the late '70s and early '80s. It's stop-motion animation in the same vein as other Rankin/Bass-produced holiday favorites such as "Rudolph the Red-Nosed Reindeer" and "Santa Claus Is Coming to Town", among others. They made quite a few Christmas holiday favorites, but "Mad Monster Party?" was their only Halloween-themed production. It features the voice (and animated likeness) of Boris Karloff as Baron Boris von Frankenstein, who wants to retire from the "science" business (also, he has created a matter-destroying device that has the potential to annihilate the world, and he doesn't want it to get into the wrong hands). He sends out invitations for a party - a Mad Monster Party - where he will elect his successor. Those invited include Dracula, The Invisible Man, Jekyll & Hyde, The Wolfman, The Mummy, The Hunchback and The Creature (you know, the usual people you would want to entrust with a world-destroying device)...oh, and Dr. Frankenstein's nephew, Felix Flankin, was also invited.
Harvey Kurtzman, who created MAD Magazine in 1952, co-wrote the screenplay to this movie, hence the "mad" in "Mad Monster Party".