Happy Halloween, Scooby Doo! is a children's Halloween themed movie that became a symbolic revival of the Scooby Doo! animated franchise that consists of many animated television series, live-action films, and comic books for today's generation. Based on the animated franchise, the film combines the theme of Halloween and the mystery genre as five friends, Shaggy, Fred, Velma, Daphne and Scooby Doo, try to solve a mystery of gigantic proportions and save Crystal Cove.
This movie takes a twist on traditional Scooby Doo cartoons, as it features special guest star Bill Nye the science guy and Elvira, two allies that help the gang on their quest to solve the latest Halloween mystery. New monsters and new villains arise as the Mystery Inc. gang try to solve their biggest and scariest mystery yet.
One noticeable reference to the Halloween season is that ordinary pumpkins in their patch turn into monsters because of a mixture of toxic waste and Dr. Crane's fear formula from one of his disabled drones. Children can easily recognize this movie as a Halloween movie because of the animated Jack-O'-Lantern monsters — or should we say, the Jackal Lanterns — chasing Scooby Doo and Shaggy, who both act like total scaredy pants. The Jackal Lanterns are also seen at the Halloween parade in the opening scene of the film; the haunted scarecrow, who is Dr. Crane in disguise, is literally scaring the civilians and using energy balls to destroy Crystal Cove.
The Giant Jackal Lantern monster that hijacked the original Mystery Machine — the Mystery Inc. gang's van — is the scariest monster children have seen in this film. This monster literally eats innocent people. Though this monster looks real and deadly on the outside, it is actually a machine, along with the rest of the Jackal Lanterns that are actually just drones. Still, the exciting parts of the movie are the animated Jackal Lanterns that give a good scare to viewers.
Bill Nye the Science Guy appears in the movie as everyone's favorite special guest star. In this film, Bill Nye has invented a new and improved vehicle called "Mystery Machine X", a more advanced technological version of the original Mystery Machine, when the old vehicle gets destroyed. Bill Nye's 2-D animated appearance perfectly resembles how he looks in the real world. His personality and love of science and technology is also shown in several scenes, most noticeably in the credits scene, where he helps the gang repair the damaged Mystery Machine. Bill Nye the Science Guy guest stars as himself, a beloved character in our world.
Elvira is the second guest star to make an animated appearance in the film. She makes her first appearance in the opening scene where the Halloween parade takes place and shows up in many scenes after that. Elvira is played by Cassandra Peterson and is the host of Elvira's Movie Macabre, a horror movie television program. Cassandra Peterson guest stars as Elvira, the original character from her popular show. Since Elvira's character ties in with the horror and science fiction genres related to the movie, she plays a major role with helping the gang.
Several running gags from the television series appear in this film. One noticeable gag that viewers find enjoyable is the repetition of chase scenes. The chase scenes usually occur when the monsters hunt the gang. When the Jackal Lanterns go after everyone, including the Mystery Inc. gang, a long car chase breaks out where people need to be rescued. The Mystery Machine X vehicle takes the chase scene to a whole new level, with Bill Nye getting involved in the action.
Another gag within the film is the unmasking of the people pretending to be either the monsters or the civilians. This gag is seen several times in the film. The gang exposes the Scarecrow as Dr. Crane and the fake Sheriff as Cutler Toe, head of Toe Omnitech. Finally, Elvira reveals the spidery face behind her beautiful mask. The unmasking of the criminals showcase the villains' abilities to disguise themselves as enemies the civilians don't recognize in order to hide their misdeeds.
Like other Scooby Doo movies, Happy Halloween, Scooby Doo! carries its traditional 2-D animation style even to this day, a classic look used in several television episodes within the franchise and loved by many.