The Mummies of Guanajuato aka Las momias de Guanajuato sees Santo team up with Mil Mascaras and Blue Demon to battle some mummies! It builds on Santo being a legacy character as seen in previous movies.
The film opens with a tour guide named Pingüino showing a group of tourists the “mummies” that Guanajuato is famous for. A special group of mummies is in a separate room: their faces are decayed but their bodies are still robust. Pingüino says the biggest mummy was a wrestler nicknamed “Satán,” who lost a championship match to Santo one hundred years earlier. He made a deal with the devil to return to life and challenge the silver-masked wrestler…and that 100 years is up now!
After the tourists leave, Pingüino thinks he sees Satán’s hand move, and he faints, dreaming that the mummies come to life. But when he is awakened by the night watchman of the cemetery, the mummies are still on their pedestals.
Pingüino goes to a local nightclub, where he tells his friends Lina and Alicia about his experience. They don’t believe him, but when they visit the cemetery, the mummy Satán is gone! The trio goes to see Blue Demon and Mil Máscaras- Lina is Mil’s girlfriend. The wrestlers are dubious but Mil agrees to go with Pingüino to look.
Meanwhile, Blue Demon is knocked out by Satán, who then enters the arena and remembers a match with Santo, in those days Satán did not have a mummy-face, – he is wearing a red mask. He kills the arena watchman and leaves, killing an old man in the park. Two young people witness this, but the police don’t believe them.
Later, Satán murders Pingüino in his bed. Mil Máscaras suggests that they call Santo, but Blue Demon demurs, saying that’s what the killer wants. Suddenly, Alicia, Blue Demon, and Mil Máscaras are attacked by three mummies. Unable to defeat their undead opponents, the wrestlers flee.
Alicia, Lina, and Julito–Blue Demon’s adopted son–are all staying at Mil Máscara’s house for safety. Blue Demon goes into another room and is promptly knocked out by Satán, who then steals the wrestler’s mask and outfit. Satán turns the costume over to another mummy, and says “You will take Blue Demon’s place.”
The police inspector in charge of the case suspects that the murders are being committed by a crazy wrestler: “Sometimes they get hit with blows that could be fatal. Many times they lose their minds.” They get a note telling them where they can find the killer that night: when they arrive, they see “Mummy” Blue Demon killing a man. He kills a policeman too, then escapes. An all-points bulletin goes out for Blue Demon, the murderer.
Blue Demon and Mil Máscaras decide to go the cemetery and have a showdown with the mummies. Julito stows away in their trunk, but when they stop to investigate a suspicious shadow in an alley, the boy is kidnaped by one of the mummies. Back at Mil’s house, Alicia is killed and Lina kidnaped by the crusty villains. The mummies are so fast, they manage to get Julito and Lina to the cemetery before Blue Demon and Mil Máscaras arrive by car. The two wrestlers are captured and thrown into a room with their friends.
Meanwhile, Santo and his manager González decide to stop for the night in Guanajuato. As they enter the city, they are attacked several times by the mummies, who apparently have left the cemetery and are wandering around terrorizing the populace. After a futile battle, Santo and González hop back in his car and drive off. But once again, the mummies are pretty fast, because they are all back in the cemetery by the time Santo pulls up in his sports car.
Santo, Blue Demon and Mil Máscaras fight the mummies with little success, until Mil retrieves three flamethrower-pistols from Santo’s car. These work pretty well, burning up the mummies. Lina says “we would have avoided a lot of problems if you’d called Santo!” Santo tells her: “Consider it a horrible nightmare. The good thing is that we’re all safe.”
As the film ends, Lina and Mil Máscaras (in his green dune buggy), González and Santo (in his gold sports car), and Julito and Blue Demon (in his green MG) drive away.