Misadventure of Mighty Plumber
Mario and Luigi are at Toad's house, watching their favorite television show, when Luigi cowers in fear of what is going to happen to the woman on TV. Mario complains about Luigi overreacting about the show, which they are watching on a TV they had brought from Brooklyn to the Mushroom Kingdom to watch. The TV is seen with a woman in front of a sink, from which some strange green slime is being produced. Luigi shouts at the woman to call Mighty Plumber, which she immediately does. Just as it looks like the slime, which has formed into a monster, is going to get the woman, the show cuts to a commercial. Mario and Luigi think about how Mighty Plumber will be able to save her.
Meanwhile, at Kastle Koopa, King Koopa appears to be doing some sort of exercise by jumping up and down, when Big Mouth and Bully appear and join him. Koopa shouts that he is having a tantrum, not doing exercises; this is because of the fact that he found a map leading into the Pipe Land Treasury, but he knows that Mario and Luigi will manage to stop him if he attempts to go there. At that moment, Hip and Hop run in and inform him of what Cheatsy is doing: using his magic wand to make the toys in commercials magically come out of the television.
Cheatsy zaps out a race car for Hip and Hop, to Koopa's annoyance. But then, Koopa sees that The Adventures of Mighty Plumber comes back from commercials, and Mighty Plumber saves the woman that was seen earlier. Koopa gets the idea to blast Mighty Plumber out of the television and trick him into helping him get rid of the Marios. He takes Cheatsy's scepter and zaps Mighty Plumber out of the TV, then tells him that two "evil plumbers" are trying to steal the gold Coins from the Pipe Land Treasury, and that his help will be necessary in bringing the Coins to his castle to keep safe, to which a naïve Mighty Plumber agrees.
Back at Toad's House, the Marios' TV is on the fritz, and the distracted brothers do not notice a Fire Piranha Plant outside, until it spits flames through the window and at the wall. The ashes read "Robbing Pipe Land Treasury - Dare you to stop me... Your Enemy, King Koopa!" Mario says that they must stop Koopa, as Mighty Plumber would.
King Koopa and Mighty Plumber are in Pipe Land, in front of the Underground Maze of Pipes, the entrance to the hidden treasury. Mighty Plumber cracks open an entrance, only for water to spew out all over Koopa. He decides to wait elsewhere, and thinks about what to buy with his Coins, but is soon interrupted when Mario and Luigi arrive. Koopa tells Mighty Plumber that the "nasty" plumbers are here, only for the brothers to ask for an autograph. However, Mighty Plumber attacks them with a plunger, and they leap away several times.
Eventually, they jump into a water-filled Warp Pipe, and Mighty Plumber sends down his plumber's snake. Luigi stuffs it into a smaller Warp Pipe growing out of the side and they swim further into the pipe. The snake re-emerges out of the other end of the Pipe, which is right behind Koopa. It grabs a hold of him and he pops out the other end, at which point he tells Mighty Plumber to stop "fooling around", as their time to get the Coins in the treasury is minimal.
In the underground maze, Mario and Luigi remember Koopa's message about robbing the treasury, and try to get there as soon as possible, only to find two pairs of footprints ahead of them. After following the footprints and going through a pipe, Mario and Luigi look around and hear Koopa's voice, talking about the vault being nearby. Luigi worries that Mighty Plumber's show will be canceled if he steals the Coins, but Mario hatches an idea to steal Koopa's map.
Luigi then taunts a Venus Fire Trap until it pops out of a Warp Pipe. It attacks Luigi and Mario struggles with it, but it bites Luigi on his rear end, until the back of his overalls are clamped in the plant's mouth. Mario uses the Venus Fire Trap's stalk as a rope and lowers Luigi down another Warp Pipe - however, Luigi's pants rip and he falls right before Koopa. Luigi grabs the map and runs off, when Koopa tells Mighty Plumber to attack him.
Mighty Plumber tosses his plunger at Luigi, and Koopa snatches the map back. Mario jumps down the Warp Pipe and stomps Mighty Plumber's foot, grabbing hold of the plunger. He throws it in Koopa's eye and grabs the map. A chase scene through the maze then begins the song "Chill Out". When the chase ends, Mario finds that Koopa and Mighty Plumber somehow got ahead of them via a Warp Pipe when their footprints are marked beyond their path.
Sure enough, King Koopa and Mighty Plumber reach the Treasury, and Mighty Plumber breaks the door open. Koopa runs in and uses his scepter to force all the coins into his burlap sack. A sort of security system that triggers a flood goes off, and Koopa, figuring Mighty Plumber has fulfilled his purpose, reveals the truth and abandons him. Mario and Luigi appear in a gap in a high end of the wall. Mighty Plumber calls himself a disgrace to the profession of plumbing, but Mario and Luigi tell him that he is their hero, and that they learned great tricks from him like the pipe battering ram, which they immediately use - they stuff a clogged pipe into one of the pipes spewing water until it blasts out and breaks the door down.
Just as Koopa is about to exit the maze with the coins, Mighty Plumber throws his plunger, now attached to a rope, at Koopa. He yanks on the rope, but Koopa stomps the plunger and breaks it. He jumps into the Warp Pipe leading to Kastle Koopa with the money, although Mario and Luigi quickly turn the crank of a Warp Pipe that sprays water into the one Koopa used to exit. Just as Koopa begins celebrating, the water floods his castle and sends him plummeting into a hole in the floor. Cheatsy sees the money Koopa dropped and tries to grab it, but runs away when the three plumbers show up. Mighty Plumber uses his snake to grab Cheatsy by the tail, and Mario tells him to send Mighty Plumber back into the television. Cheatsy does so, and Mario grabs his scepter so that no more television-related mischief will happen. The bros. then return the money to the treasury where it belongs.
Later at Toad's house, the Mario Bros. are watching Mighty Plumber when the title character gives them a thumbs up. Mario proudly tells himself and Luigi that they are real heroes.
Animation and continuity errors
Names in other languages