Weekenders Adventures of Alvin and the Chipmunks Meet Frankenstein is the first Weekenders/Universal Studios crossover film made by Sonic876. It will appear on Google Drive in the near future.
The Chipmunks are performing at a theme park called Majestic Movie Studios, a spoof of Universal Studios Hollywood "Things Out There." After one of their shows, in which Alvin accidentally scares a small boy, they go off for a break. Meanwhile, Doctor Frankenstein has come and is inhabiting a new attraction called "Frankenstein's Castle" as he makes another monster. The Chipmunks get lost, and eventually get locked inside the park (not to mention, they missed their show, so it was canceled). They find that one light is still on, in the castle, where Dr. Frankenstein is working on the monster. The Chipmunks witness the monster being resurrected. But Theodore drops his teddy bear, and when Alvin gets it, Dr. Frankenstein steps on his cap (Alvin hates when people touch his cap). He sends the monster after them on a wild goose chase through the park. Eventually, they end up on a roller-coaster with the monster on their tail. They lose him when he gets scared and stops the car, then when he finally lets go, the car lurches forward going faster than the ride was engineered. This causes the roller coaster to go off its tracks into the park sidewalks. They climb out and run out of the park. In the ruckus, Theodore drops his teddy bear, and the monster finds it.
When the boys get home, they try to tell Dave what happened but he doesn't believe them. They then go up to their room, get ready for bed "If a Monster Comes in Our Room," and go to sleep, and the monster finds their house and returns the teddy bear to Theodore. It starts to rain, and Theodore feels bad for him, so he lets him sleep in his bed that night. The next morning, Dave goes to the park to consult with the manager to book them for the premier that night of the new Bud Wiley movie. Meanwhile at home, the Chipmunks take the monster (Theodore refers to him as "Frankie") to the park and teach him about being kind and making friends "If You Wanna Have Friends." When the sun is setting, the four are heading home to cook dinner for Dave. They make lasagna, but Frankie accidentally takes it out of the oven without gloves and burns his hands. In the process, he throws the lasagna out the window. Alvin goes out to retrieve it, but is kidnapped by the Doctor and taken to his lab in the theme park. Dave comes home, and Simon and Theodore, are told by him they are playing at the premiere. They then run off to the park with the monster to rescue Alvin.
At the park, Dr. Frankenstein makes Alvin drink a purple concoction. Then the doctor electrocutes him with 50,000 volts to "complete the process" as he says. The Chipmunks then burst through the door and knock over a few bottles of brains to distract Dr. Frankenstein as they rescue him. When they get out, Simon steals the book Frankenstein was using. He reads that the doctor fed him "Cartoon Monster Maker" which instructs to serve cold with 50,000 volts of electricity, then to wait three minutes. Simon checks his watch. The three minutes are up. Just then, Alvin grows to an enormous size, then shrinks down to his normal size. But he is not his normal self, and now resembles a cartoon character. He has a spiral for one eye, and his nose has grown and it is shiny. He runs away in a cloud of smoke.
At the premiere, he causes chaos, like a crazy cartoon character. He destroys a table with a chainsaw, defaces the movie's poster, and pops inside peoples wardrobe and messes up their hair. Simon and Theodore make an antidote from food on the buffet and go to feed it to him. But he must be upside down for it to work. When Bud Wiley arrives, Alvin closes his autograph book around his face. Bud begins chasing him, and they end up on top of a cut out of Wiley 100 feet in the air. Alvin is upside down when it begins to collapse, so Simon and Theodore throw it at him, and he drinks it. When he becomes normal immediately, he helps Bud by holding on to him when he almost falls. Dave and the boys make a trampoline out of a tablecloth and rescue them both.
In the theater, Dr. Frankenstein manages to sneak in dressed up in a costume of Sammy Squirrel (the park's mascot, whom he despises) after being denied entrance to the party. He sees that Alvin is cured, but realizes if he shocks Alvin, he can turn him back. He turns the mic to a high revere so when Alvin touches it, he would be shocked. But then the Monster turns up, and grabs the doctor. As he is carrying him, he slips and Dr. Frankenstein grabs the microphone to steady himself and gets shocked. The people see the monster and start to run away from him, but Theodore tells everyone if they are kind to him, he will be kind to them. Dr. Frankenstein awakens and tries to get the costume off, but can't.
In the end, Dr. Frankenstein is now the new entertainer, still stuck in the Sammy Squirrel costume, the Monster gets a job as a bus driver for tourists around the sets (though since Alvin taught him how to drive, he is a rather reckless driver, not to mention he has a chipmunk voice). At night, the sounds are still heard in Frankenstein's Castle.