In the frontispiece of I, Monster, a turtle (presumably Donatello) stands in a laboratory, operating on the monster of Frankenstein. In the Treasury Edition's, Don compliments Mikey on his way with words, as a silhouetted Frankenstein monster lurks in the background.
In the first Flaming Carrot crossover, Frankenstein’s disembodied head escaped from the Museum of Natural History. A former employee explains that the head came in with a shipment of artifacts that were saved from Nazi destruction during WWII. The head, still alive, eventually learned how to roll like a beach ball and escaped. Frankenstein’s Head, having spent decades in a museum, is now well-learned in the mystic arts (though he still yearns for a new body) and teams up with the Evil Umpires gang to levitate the Empire State Building and steal it from New York.
Robert Babo King of the Evil Umpires asks Frankenstein’s Head to use his magical abilities to levitate the building. The Turtles, Carrot and Screwball attempt to stop their plan. Raphael snatches Frankenstein’s Head and the Turtles play a game of keep away with it.
Finally, Carrot tosses it to Screwball and tells him to fly away with the noggin on his rocket boots before he can levitate the building. Frankenstein’s Head mentally attacks Screwball with thought power and Screwball responds with his own mental attacks. The two are locked in telepathic battle until Screwball’s pet shoelace crawls inside Frankenstein’s Head’s ear and tickles him. The momentary lapse of concentration hands Screwball the victory and he flies off with him.
Frankenstein’s Head recites a spell and vanishes from Screwball’s hands. Frankenstein’s Head’s spell, intended to give him the body of vicious Viking Rudolf the Remorseful, failed. Frankenstein’s Head is now stuck with the body of Rudolf the Red-Nosed Reindeer.