Every year, all of the classic Hollywood monsters (consisting of Frankenstein's monster, his wife Repulsa, a Mummy, the Witch Sisters, Bone Jangles the Skeleton, Dr. Jackyll/Mr. Snyde, Swamp Thing, and Dragonfly) gather at Count Dracula's castle in Transylvania for the "Monster Road Rally", a road race similar to Wacky Races, awarding the winner with the "Monster of the Year" award as well as many other macabre prizes as announced by Dracula's wife and co-host, Vanna Pira. However, this year, Dracula receives a postcard from the Wolfman stating that he has retired to Florida and thus will not be participating in any further races.

Dracula fears he will have to cancel the race due to this sudden absence, until his lion-like manservant Wolfgang notifies him of a way to create a new werewolf: according to an old spellbook, the full moon will come into the perfect position to transform a human into a werewolf every five centuries, on three nights in a row that begin the following night. The one in line to become the next werewolf is revealed to be none other than Shaggy Rogers, whom coincidentally has won a recent car race with the help of his pit crew, Scooby-Doo, and his young nephew Scrappy-Doo.

Dracula sends his hunchbacked henchmen, "The Hunch Bunch" (consisting of the well-civilized Brunch and the gibberish-speaking Crunch), on a mission to America to turn Shaggy into a werewolf and bring him back to his castle for the race. The first two nights, the duo is unsuccessful, but on the final night, while Shaggy is at a drive-in movie along with his girlfriend Googie, the Hunch Bunch manages to expose Shaggy to moonlight by dropping the sunroof of his customized race car, causing Shaggy to be transformed into a werewolf. However, Shaggy's hiccups surprisingly force him to alternate between human and werewolf. Hearing the other movie watchers speaking of a werewolf loose in the theater, Scooby hides in a nearby car. Upon meeting Scooby and seeing his reflection, Shaggy flees the drive-in with his car with Scooby, Scrappy, and Googie in tow, pursued by the Hunch Bunch, but loses his hiccups in the pursuit and thus remains trapped in werewolf form. The Hunch Bunch then knocks the group out with moon dust from their vehicle, the "Bat-Copter", and fly back to Transylvania, towing the car.

Revealing himself, Dracula explains to Shaggy why he was transformed, but Shaggy, having no desire to be a werewolf, refuses to participate in Dracula's plans. After several failed attempts to extort Shaggy, Dracula offers him a bargain: if Shaggy agrees to drive in the race and wins, Dracula will change him back to human and allow him and his friends to leave. The deal is made, but Dracula has no intent on allowing Shaggy to succeed.

The gang is then given good lodgings, treated as guests in the castle, and allowed all the food they wish for breakfast. Dracula then shows them the trail that Shaggy will have to follow for the race and consents to let them navigate the track in their own racecar, with the "Werewolf Wagon" currently undergoing maintenance for Shaggy. Dracula attempts to rig the track by sending the Hunch Bunch to implement traps, but despite their efforts, Shaggy completes the course expertly, making the Count worry that he may lose his new werewolf. He subsequently alters the racecourse, sabotages the Werewolf Wagon, and has the Hunch Bunch deprive Shaggy of sleep.

The next morning, Googie energizes Shaggy with a kiss, and he repairs the Werewolf Wagon shortly after the race begins. Everyone conspires against Shaggy and Scooby throughout the race, but thanks to Googie and Scrappy, who follow along in their own car as their pit crew, Dracula, the Hunch Bunch, and the other racing monsters end up doing more harm to themselves than him. After more failed attempts, Dracula loses his patience and unleashes his secret weapon, Genghis Kong, a towering ape-like beast, to stop Shaggy. As the other racers near the finish line, Googie and Scrappy return and rescue Shaggy and Scooby, then both pairs work together to make the monster fall onto the other cars, leaving an easy path to victory for Shaggy.

Furious to see all of his schemes have failed, Dracula goes back on his deal, stating that there is no way to turn Shaggy back. However, after Vanna Pira reveals that the solution is in Dracula's spellbook, the gang steals the book and make an escape. Dracula chases after them in his weaponized car and later his own plane. The four barely manage to dodge Dracula's powerful gadgets, and seconds before Dracula gets the best of them, a thunderstorm ensues. Dracula's plane is struck by lightning, sending him plummeting into the ocean below, where a shark chases him off.

Returning home, Googie uses the book to change Shaggy back to human. That night, the gang all sit down to watch another horror movie and eat pizza. In the final scene, Dracula and the Hunch Bunch sneak up to their window swearing revenge, ending the film on a cliffhanger.

• Don Messick as Scooby-Doo and Scrappy-Doo
• Casey Kasem as Shaggy
• B.J. Ward as Googie, Repulsa and Woman on TV
• Hamilton Camp as Count Dracula, Police Officer and Man in Drive-In
• Jim Cummings as Frankenstein, Dragonfly, Wolfgong, Snack Bar Manager, Genghis Kong and Monster on TV
• Joan Gerber as Short Witch Sister and Woman at Store
• Ed Gilbert as Dr. Jackyll, Mr. Snyde, Spooky Voice, Doorknob and the Narrator
• Brian Mitchell as Bonejangles
• Pat Musick as Vanna Pira and Girl in Drive-In #1
• Alan Oppenheimer as Mummy and Swamp Thing
• Rob Paulsen as Brunch, Ghost and Man in Car
• Mimi Seton as Tall Witch Sister, Girl in Drive-In #2, Boy in Drive-In and Screamer
• Frank Welker as Crunch, the Spider Monster, Plant Monster, Tyler Country Racer #1, Rooster and Schlockness Monster

The film was originally released in 1991 on VHS by Goodtimes Home Video and got re-released by Turner Home Entertainment in 1992. It was released that same year on Laserdisc by Image Entertainment. Warner Home Video re-released the film on VHS and DVD in Region 1 on March 5, 2002.^[1]

The film was released on Blu-ray on February 20, 2024, as an individual release, and as part of a Hanna-Barbera Superstars 10 boxset through Warner Archive.^[4] Scooby-Doo and the Reluctant Werewolf was produced using an early form of digital ink and paint, and was output to a final 1" videotape master, with no film protection of any kind. This presentation has been up-converted from its original analog standard definition master to digital High-Definition, with every effort made to improve the visual quality of the program.^[5]

On Rotten Tomatoes the film holds an approval rating of 20% based on 5 reviews, with an average rating of 5.0/10.^[6] Common Sense Media gave the film a two out of five stars, saying, "Typical Scooby tale has lots of jokes and cartoon jeopardy."^[7]

• Scooby-Doo! and the Reluctant Werewolf at IMDb