The franchise My Pet Monster began with the cult classic boys' toy of the 1980's of a furry blue monster with golden horns, pinkish purple eyebrows and muzzle, a bumpy green nose that appears akin to a pickle, yellow eyes with green pupils, a navy underbelly with ridges, and (Other brands that started as toys before creating their cartoons: Winnie the Pooh, The Adventures of Raggedy Ann & Andy, Teddy Ruxpin, Care Bears, Pound Puppies, He-Man & The Masters of the Universe, My Little Pony, Strawberry Shortcake, G.I. Joe as an all-American patriotism series, and both giant robot series Transformers & Voltron).
However, before the 1 season cartoon with 13 episodes of My Pet Monster came to be, there was a kind-of obscure live-action, direct-to-video movie of B-quality loosely based on the blue fuzzball.
As far as recognizable actor faces go in the film, the outgoing sister with a Punky Brewster personality opposite her introverted, near-sighted brother as our put-upon as well as unfortunately generically named ("Max Smith" is the stereotypical, bland name chosen) title hero was portrayed by a young Alyson Court (her supporting role as Melanie Smith was done before her 1989 voice over role as the animated version of Winona Ryder's Lydia Deetz from Tim Burton's "Beetlejuice", a cameo during the "Easy Going' Day" song sequence of "Sesame Street Presents: Follow That Bird", and her young adult job as funny clown Loonette on PBS kids' show "Big Comfy Couch") and recognizably-accented Colin Fox portrayed mainstay villain Dr. Eugene Snyder who, upon completing the painstaking relocation & restoration of the Babalonyan era monster statues engraved with inscribed tribal markings (they were then later transcribed & translated by Dr. Snyder for use in his scientific research), kept insisting that "these statues possess the power to transform anyone who stands in front of them into monsters" (to his highly-skeptical fellow scientists, this radical belief appropriately resulted in Dr. Synder's early dismissal within the scientific world alongside a loss of dignified credibility) so often that the only job he could get was as a Remedial History of Art & Sciences museum tour guide, which he deeply resents whilst trying to find suitable validation/proof to support his seemingly crackpot assertions.
As luck would have it, Dr. Snyder's future vindication would unknowingly be part of Mr. Blair's class on a field trip to the museum from their nearby school on Park Street, as upon losing his sandwich ("Mango & Peanut Butter, my favorite") due to the museum's strict "No Eating" policy after being caught by Dr. Snyder and then, getting the apple that his sister Mel covertly slipped to him during Dr. Snyder's expository monologue knocked free from his hand (which happened when he nonchalantly & sarcastically insulted class clown Bernie's suck-up sidekick who always agrees with Bernie on everything like any true toad does their usually abusively demanding bosses, depicted here with what even notable online critic Doug Walker perceived as hidden sexual tension, since these are, after all, young adolescent preteen children we're dealing with), Max Smith - the blank slate nobody he is - would come face to face with the stone monolith resembling the aforementioned toy the film & subsequent cartoon would each be very loosely inspired from.
Following some hokey lightning effects even for its time (as the film plods along to diverge into two plots arcs, a full X-Ray vision animation effect would also yield the same result as Dr. Snyder witnesses the transformation first-hand later on) and "Max Smith, former boy" has BECOME My Pet Monster (granted, the conceptualized end design for the monster itself was a lackluster flop, depicted as a sub-par character costume just shy of being a school's team mascot that just barely resembles the toy it's based on), only for Dr. Snyder to goad them into dog cages to haphazardly blend Max's monster issue (which is conveniently driven by intense hunger with a growling stomach as a warning sign before the change) together with the boring dog-napping sub-plot that overshadows the actual point of the movie (taken verbatim from the movie after Max's monster design scared Tippy, the accredited pedigree'd poodle mix of apparently well-to-do socialite Stephanie Summers aka the high-end as well as high-strung girlfriend to Rod, the teenage older brother of Max & Mel, who sees himself as a ladies' man: "What could be a bigger problem than a brother who turns into a monster?" "A girlfriend who turns into a she-wolf!") until the anti-climatic scenes when Max as the monster stops the two dog-nappers who took Tippy from the Summers' and renamed her to Coquette Dubois from making their getaway with the stolen money that was quickly transferred back to the Summers' accounts, with Tippy back into Stephanie's doting arms). To conclude, Max & Mel weigh the con vs pro merits of Max's transformations into the monster, with Mel wishing for him to be able to change whenever wanted or Max just clinging to the false hope that he could be cured of the whole debacle.
The cartoon maintains the same performers from the original film as voice actors under different names (Mr. Hillard = Dr. Snyder, Jill = Mel, Princess the Pooch = Tippy, etc.)and separates Max from the monster using the META concept of making "Monsie" an actual toy through the viewing lens of the cartoon, and whereas the film ends with Dr. Snyder lamenting his inability to produce a monster to back his earlier findings, just prior to his own stomach growing whilst standing in front of the Beastor statue, thereby inferring that he was BECOMING Beastor if a live-action continuation was made instead the cartoon.