Once a horror franchise gains momentum and finds an audience, it’s only a matter of time before sequels are no longer enough to satisfy its audience – the next step is a crossover. From Frankenstein Meets the Wolf Man and King Kong vs. Godzilla to Freddy vs. Jason and Alien vs. Predator, monster crossovers have a proven track record at the box office, attracting fans from both original franchise camps as well as new viewers who are curious to the trend. In 1958, American International Pictures took advantage of the teenage monster film craze and released a different kind of crossover film called How to Make a Monster.
How to Make a Monster stars Robert H. Harris (Valley of the Dolls) as Pete Drummond, a movie special effects makeup man for American International Studios who, while working on his latest movie, is fired as the studio heads intend to steer the studio away from horror movies. Pete does not take his dismissal lying down, however, and comes up with a plan that involves hypnotizing two actors named Tony Mantell (Gary Conway from “Land of the Giants”) and Larry Drake (Tombstone’s Gary Clarke) while he applies makeup to them. 
With a little help from his assistant, Rivero (Paul Brinegar from High Plains Drifter), Pete finds himself with a Teenage Frankenstein and a Teenage Werewolf who will do his murderous bidding. When bodies start piling up around the studio, the authorities start to get suspicious, but when an eyewitness describes Larry’s Teenage Frankenstein character as the murderer, Pete really finds himself in hot water. Trying to stay a step ahead of the police, Pete works towards his ultimate goal of revenge.
How to Make a Monster is not a typical crossover film. For one, the films that it mixes, I Was a Teenage Werewolf and I Was a Teenage Frankenstein, were made just a short year before. Also, it deals with the behind-the-scenes making of the two films that it mashes up instead of the original plots themselves. 
Finally, the monsters are not the main antagonists in the film, but more like puppets; the real villain is neither the Teenage Werewolf nor the Teenage Frankenstein, but Pete himself, their creator.
In typical crossover film fashion, How to Make a Monster took many resources from the source films. Not only was it made by American International Pictures, which distributed I Was a Teenage Werewolf and I Was a Teenage Frankenstein, but it was also produced by the same man, Herman Cohen (Blood of Dracula). It was written by Cohen and Aben Kandel (Konga) who, under pen names, wrote both Teenage Monster movies, and was directed by Herbert L. Strock (The Crawling Hand), who also directed I Was a Teenage Frankenstein. AIP prided itself on its ability to reel in the younger viewers and, riding on the success of its predecessors, How to Make a Monster continued the trend.
Although Robert H. Harris gets top billing, and his Pete Drummond is the focal character, the two teenage monsters are who really sell How to Make a Monster. Gary Conway reprises his role from I Was a Teenage Frankenstein and Gary Clarke takes over the Michael Landon part from I Was a Teenage Werewolf, and both actors make great monsters as well as unwitting victims. Conway and Clarke are the heartthrobs that sell How to Make a Monster to its target teenage audience.
Taking a page from legendary director William Castle and borrowing further from I Was a Teenage Frankenstein, How to Make a Monster has a gimmick; although most of the film is in black & white, the last reel of the film is in color. As jarring as it is, the switch to color does not feel forced. On the contrary, it feels as organic as the change in The Wizard of Oz, providing the audience with an amusing little “a-ha” moment just before the climax of the film. The lobby cards for How to Make a Monster tell the audience that they will “see the ghastly ghouls in flaming color!” and the film delivers on the promise.
Whereas many crossover films, both old and new, seem more concerned with doubling the audience than presenting a compelling story, How to Make a Monster simply inserted movie fiends from other films into itself in an original way. Because of this, the film is more than just a sequel or an offshoot; it stands on its own as a classic horror movie.