The Man with Two Brains
(1983)

POOPER:
Merv Griffin (playing himself) is the 'elevator killer.'

LITTLE LONGER:
Merv kills Delores (Kathleen Turner), the evil wife of Dr. Hfuhruhurr (Steve Martin).

The good doctor transplants the brain of Miss Uumellmahaye (voiced by Sissy Spacek) into Delores' body.

They live happily ever after, even though it turns out that Miss Uumellmahaye was a compulsive eater, and Delores' formely sexy body becomes grossly obese.

Thanks Curt (Pooper) and John L (Longer)!

IMDB