Scooby-Doo! and the Monster of Mexico is a 2003 American direct-to-video animated adventure film; the sixth in a series of direct-to-video films based upon the Scooby-Doo Saturday morning cartoons. It was released on September 30, 2003, and it was produced by Warner Bros. Animation.
It is the second and final film (after Scooby-Doo! and the Legend of the Vampire) to briefly reunite the surviving or available voice cast from the original 1969 series, with Frank Welker voicing Scooby-Doo in place of the late Don Messick. The film also marks the last time Nicole Jaffe and Heather North voice Velma and Daphne, respectively, before North's death on November 29, 2017.
Plot
Fred's pen-pal, Alejo Otero, who lives in Veracruz, Mexico, invites Fred and the rest of the gang to visit him and his family there. Mystery Inc. talk about it until they decide to go. However, after Alejo sent the invitation to Fred, a big long-haired monster started to terrorize the population of Veracruz. Alejo and his young son, Jorge, and their pet Chihuahua, Chiquita, see the monster, and the locals start calling him "El Chupacabra".
Later, when Mystery, Inc. arrives in Veracruz, they meet Alejo, who run a huge and fancy hotel, and he shows them around and where they will be staying. He then introduces his family, which includes his wife, Sofia, his mother, Doña Dolores, his brother Luis, and Luis's fiancée, Charlene, who is originally from the United States. While the gang and the Otero family enjoy a meal, Diego Fuente, a man who did business with Alejo and Luis’ late father, arrives to speak with the brothers about buying hotel, but they refuse. Fuente leaves, and the family go inside when a fierce storm arrives. When inside, Alejo's forced to tell the gang about El Chupacabra, and says that he does not have many other guests besides the gang because El Chupacabra has been scaring them away.
During the night, Shaggy and Scooby-Doo are scared when they think they hear a noise. They then hear a loud growl and run screaming out of their cottage. After seeing footprints outside of Shaggy and Scooby's window, Fred declares that there is a mystery they have to solve. The next day, the gang and the Otero brothers set out to search for El Chupacabra. Daphne interviews the townspeople, but none of them are able to find El Chupacabra. When they get back to the Mystery Machine, they find someone has written a threat written in Spanish on it, warning them to get out of solving the mystery. The gang realizes this is serious and decide to search at night. Fred, Velma and Daphne go one way, Alejo and Luis go another way, and Shaggy and Scooby stay at the Mystery Machine.
At night, Shaggy and Scooby sleep in the van, while someone drains their brake fluid. Fred, Velma and Daphne search the woods, and find El Curandero, a medicine man. El Curandero tells them they need to look at history and that they are in grave danger. Meanwhile, Alejo and Luis are searching when Alejo sees El Chupacabra. Alejo is chased and nearly falls off a cliff. He calls for Luis, but there is no answer. El Chupacabra disappears, and Luis shows up, saying he was knocked on the head by El Chupacabra.
Shaggy and Scooby start driving, but then realize they cannot stop due to the brake fluid tank being tampered with. They meet up with Fred, Velma, Daphne, Alejo and Luis, who were being chased by El Chupacabra. Eventually, the Mystery Machine runs out of gas and stops right in front of a gas station, where they got it fixed. The gang drives along and finds a sign to a history museum, and thinking that is what the medicine man said, go to it. When they get there, they meet a suspicious and hyper museum guide who leads them into an auditorium. There they see a performance about ancient Mexican customs. The guide then makes Daphne volunteer, and she kidnaps her. The rest of the gang find a secret passageway and follow it, until they come to Aztec pyramids. They find Daphne at the top of one and rescue her, but the tourists chase after them, after they are accused of destroying a statue. After a long chase scene and fights against giant living statues, they finally return to Veracruz.