The Fiesta Host is an Aztec Ghost is the second episode of The Scooby-Doo/Dynomutt Hour, later repackaged as the second episode of the first season of The Scooby-Doo Show.
Premise: The gang is in Mexico to attend a fiesta, which gets canceled because of the ghost Katazuma, an ancient Aztec king.
Synopsis: Freddy, Daphne, Velma, Shaggy and Scooby-Doo are heading to Mexico for a fiesta in the village of Cinco when they run across a huge footprint in the middle of the road. Dismissing it, they head on to the village of Cinco, which seems deserted. Behind them, a huge apparition of a giant Aztec statue stands there and roars! Unaware of the giant, they think they see someone in the plaza and Shaggy and Scooby investigate, only to be spooked by an stone Aztec statue. The gang moves for a hotel, as, unbeknownst to the gang, the statue gets up and starts walking! Scooby goes to get luggage from the van, and encounters the live statue. Scooby runs back to the hotel, trying to tell the gang what happened. A man interrupts.
The man claims he is owner of the hotel, Juan Martinez. He then explains that the giant ghost of Katazuma has been terrorizing the village and the fiesta is cancelled. He also tells about a Phantom Barge that floats down the river every night and then disappears. The gang gets ready for bed, when the Aztec statue from the plaza chases Shaggy and Scooby and when everything settles, the gang meets two archaeologists Professor Stonehack and his wife Elina, who came to the village to study the ancient Aztecs. The two tell a tale that they went to Katazuma's tomb and unleashed the ghost of Katazuma.
The Stonehacks depart and the gang just catches Katazuma materialize outside and make Professor Stonehack vanish! Stunned and curious, the gang borrow a boat from a hermit. They start floating up the river when the phantom barge appears and heads straight for the gang in the boat. It disappears into thin air. The gang go ashore and explore, finding footprints. Scooby and Shaggy depart to follow the footprints while Velma, Fred and Daphne keep heading in the way of the pyramid. Before they can follow the prints, the ghost of Katazuma appears and chases them, but the Aztec Statue appears as well, trapping the gang between. The gang flees into the jungle and arrive at the pyramid. Entering through a secret door, they find their first clue: modern electricity inside a 1000-year old pyramid. The gang splits up and Fred, Daphne and Velma find a movie projector and Katazuma, who has shrunk down to regular size. Freddy blinds Katazuma with the projector light and Fred and the girls flee.
Shaggy and Scooby discover a vacuum cleaner that blows out smoke and then when it clears, the Stone Monster arrives, and chases them until they meet up with Fred, Daphne and Velma. Katazuma makes an entrance and locks the gang inside a room. Velma reads the hieroglyphics and discovers the room was dedicated to the moon goddess. When the moonlight shines on a specific inscription, a secret passage will be revealed. Using an array of reflectors, they guide the moonlight to the inscription and a secret passage reveals. They escape the pyramid and witness Katazuma and the statue loading treasure from the pyramid onto the Phantom Barge. The gang boards the boat and as they go under a bridge, Katazuma hits a lever, causing a secret passage to open in the stone wall of the underside of the bridge. That's how the barge disappeared. So the gang devise a plan and all dress up in Aztec relics, scaring the two ghouls, but it backfires and a chase ensues before the gang sets up another plan to catch the "pyramid pests" in a crate. It backfires, again, and the goons chase Scooby, until Scooby goes skidding on a barrel and the gang places springs on the stone statue and Katazuma's feet, causing them to spring off the pier and into the water, revealing Professor Stonehack and his wife to be the culprits. They projected the fog with the vacuum cleaner and the giant ghost with the projector, and scaring everybody away, gave them a chance to rob the pyramids.
Now that the case has been solved, the fiesta can now continue and Shaggy and Scooby make the world's biggest burrito.