Toddler Terrors of Time Travel
One day at Kastle Koopa, King Koopa is sitting on his throne. He was moaning about his aching head, just as he sandwiches a hot water bottle between it and his crown. With King Koopa is Kooky von Koopa, who mentions that his father seems to get headaches every time he gets defeated by Mario and Luigi. As Koopa places a second hot water bottle under his crown, he and Kooky note that he could have taken over the Mushroom Kingdom years ago had the Mario Bros. never gone down the drainpipe back in Brooklyn. As Koopa and Kooky speak, they fail to notice Toad, who is hiding inside a flower pot, and spying on the duo through a periscope disguised as a flower. After some brief pondering, Kooky suggests that they can change history through the use of time travel, to which Koopa complies.
Later, onboard the Doomship. Kooky is making adjustments to his latest invention, the Time Travel Tube, while Koopa, who appears to have gotten over his headache, argues that it will not be able to send them back in time. Kooky implies that he knows what he is doing, just as Toad retracts his parascope and gets out of his disguise. Toad mentions that he needs to alert Mario and Luigi right away, and leaves.
Sometime later, as a team of Hammer Brothers are loading crates onboard the Doomship, Mario, Luigi and Toad arrive. Looking at one of the unloaded crates, Luigi comments that the three of them cannot fit inside it, but Mario disagrees, and forces them to squeeze inside one. Soon, a Hammer Brother picks up the crate that the they are hiding in, and complains about how heavy it is, while another Hammer Brother has no problem in carrying four crates at once. As the Hammer Brother carries the crate into the Doomship's helm, Koopa orders him to put it down against a wall. He hears Toad make a squeak from inside the crate, and goes to check it out. He asks Kooky if he heard anything to which Mario responds that it is just his imagination. Right before Koopa can inspect the crate, he is suddenly distracted by Kooky, who has managed to get the Time Travel Tube working.
Kooky states that he is going to take the two of them back in time to Brooklyn, just before noon, when the warp that sent Mario and Luigi to the Mushroom Kingdom opened up. As the Doomship takes off, Koopa takes control of the wheel, and demands that they hurry up. Kooky warns him not to rush the procedure, and sure enough, the Doomship starts shaking back and forth, eventually breaking the crate that Mario, Luigi and Toad were hiding in. Before Koopa can deal with them, Kooky, who is trying to fix the Time Travel Tube, explains that they are going too far back in time, just as the Time Travel Tube overloads, creating a large flash.
As the Doomship slows down, the flash fades, revealing that everyone onboard the Doomship has been turned into infant versions of themselves due to a glitch from the Time Travel Tube. After both sides settle into their younger bodies, Baby Kooky makes some more adjustments to the Time Travel Tube, just as the Doomship arrives in Brooklyn, and crashes in a vacant lot.
Mario, Luigi and Toad crawl out of the crashed Doomship, and Toad questions why they are still babies. Mario answers that the crash messed up the Time Tube, and that they do not have much time to get back to the apartment where they originally fell down the drain. Luigi suggests that they try to find a shortcut, while Koopa orders Kooky to follow them.
Mario, Luigi and Toad are then chased down a sidewalk by the baby Koopas. Upon reaching an intersection, Toad has to stand on Mario and Luigi's backs in order to reach the crosswalk button. When Toad pushes the button, the walk symbol on the do not walk sign turns into a baby, and the crossing guard allows them to cross. After the babies all cross the street, Koopa and Kooky get caught in a jump rope that some kids are playing with. Mario, Luigi and Toad enter a back alley and take off with a stroller, a wagon, and a skateboard respectively. Koopa and Kooky hop into a baby carriage and use it to keep up with Mario's group, whom they corner in another alley. Just before Koopa and Kooky can enter the alley, an elderly woman mistakes them for normal babies, allowing Mario's group to make their escape. However, the woman is shocked to see that the babies are not human, and she runs off screaming. When Kooky notes that the "Mario Babies" got away, Koopa claims that they need to stop "kidding around".
After returning to the Doomship, Kooky makes some more adjustments to the Time Travel Tube, and succeeds in restoring himself and King Koopa to their proper ages. Koopa then announces that they are going to carry on with the next part of his plan.
Meanwhile, Mario's group arrives at the front door of the apartment where the drainpipe is. As Mario knocks on the door, it gets opened up by the lady inside, and he accidentally knocks on her knee. Although the lady assumes that the babies were abandoned, Mario tries to explain that they are plumbers, and the babies proceed to crawl into the apartment. The lady exclaims that plumbing is too dangerous for babies, so she picks them up and places them on her bed, where she expects them to take a nap.
Just then, the lady notices that a van has pulled up outside, with the words "Koopa & Kid Costume Plumbers" crudely painted on its side, and figures that the "real" plumbers have arrived. Koopa and Kooky, both dressed in caps, gloves and overalls exit the van and walk over to the front door. Kooky explains that if they can pass off their Koopa bodies as costumes, no one will suspect that they are not from the real world. After Koopa knocks on the door, the lady opens up and is introduced to the "Costume Plumbers", who claim to make plumbing a party. Overhearing the conversation from inside the bedroom, Luigi comments that they will never make it to the Mushroom Kingdom if the Koopas mess with the drainpipe.
Inside the bathroom, the lady asks for Koopa and Kooky to fix her drain as fast as they can, so that she can bathe for her party that night. Koopa claims that they will fix everything, and escorts the lady out of the bathroom. Meanwhile, Mario is spying through the bathroom window from outside, and comments that they cannot let King Koopa get away with his plan. Toad asks what they can do, and Luigi gets an idea after looking down at the basement window.
Mario, Luigi and Toad enter the basement window, and head over to the bathtub drainpipe, which Luigi wants them to open up. Mario tries to open the pipe with a wrench, but as a baby, he is not strong enough, and needs Luigi and Toad's help in doing so. Toad asks what they are supposed to do now, and Mario picks up a hose, suggesting that they reverse the flow of the apartment's water.
Back in the bathroom, Koopa stuffs a washcloth down the drain, and demands for Kooky to find more stuff that they can use to clog the drain with. As Kooky throws some toiletries into the bathtub, he claims that they are going to make sure that the Mario Bros. never make it to the Mushroom Kingdom. As Kooky runs out of the bathroom, the lady asks how Koopa is doing, only for him to tell her to be quiet. When the lady comments that his remark was rude, she brings up the subject that they were supposed to make plumbing a party. Kooky returns to the bathroom carrying a lamp and two end tables, and comments that they are indeed making plumbing a party, and are playing a game called "STUFF YOUR FURNITURE DOWN THE DRAIN!"
Down in the basement, the pipes have been rerouted, and Mario tells Luigi and Toad to turn on several faucets, which in turn sends water up through the apartment's drainpipes. As Koopa and Kooky try to keep their clog in the drain, the lady panics as water comes spraying out of the kitchen sink, dishwasher, lighting fixtures, and other odd places. As the lady tries calling for help, water even sprays out of the phone receiver. Kooky, however, has discovered what is happening in the basement after looking through the basement window for himself.
As the water flow comes to a halt, Mario realizes that the Koopas must have shut off the water, just as King Koopa and Kooky enter the basement. Mario tells Luigi and Toad to follow him into a pipeline, but before they can pass through the first pipe, Koopa lifts it up, with both Mario and Luigi trapped inside. When Luigi asks what he is doing, he and Kooky stick a large cork into each end of the pipe, and toss it onto a table. Figuring that the Mario Bros. are stuck, they head upstairs, unaware of the fact that Toad got through the first pipe, and crawls out from inside the next pipe.
Toad travels through a hose as if it were a Warp Pipe, and comes out in the alley next to the apartment. From there, he follows Koopa and Kooky back to the Doomship, and jumps onboard just as it takes off. Meanwhile, Koopa explains to Kooky that since the Mario Bros. are now stuck in Brooklyn as babies, they can return to the present and freely take over the Mushroom Kingdom. When the Koopas' backs are turned, Toad uses his parascope to snatch the Time Travel Tube, and uses it to restore himself to an adult (although this is never shown). Toad then places the Time Travel Tube by one of the Doomship's portholes, aims it at the apartment's basement window, and fires a beam at it.
The beam hits the pipe that Mario and Luigi are trapped in, and restores them to their adult selves, causing them to burst out of the pipe in the process. With only thirty seconds left before the warp opens up, Mario and Luigi hurry upstairs and rush to unclog everything that Koopa and Kooky shoved down the drain. After pulling out the actual clog that clogged the lady's drain in the first place, the lady thanks Mario and Luigi, and invites them to her party. However, Mario and Luigi have already filled the tub with water, and Mario explains that he and Luigi have a date with the Princess. Mario and Luigi then jump into the tub and get warped down the drain along with the rest of the water.
Back in the present, in the Mushroom Kingdom, Koopa, who has his claw around Princess Toadstool's arm, is ordering her into surrendering her kingdom to him. Kooky, who is holding Toad's arm, explains that the Mario Bros. are stuck in the past, and are unable to stop them. Before anyone can react, Raccoon Mario and Luigi leap out of a pipe, startling Koopa and Kooky, who let go of Princess Toadstool and Toad. Mario then throws the clog from earlier at Koopa, who comments that this whole ordeal is even worse than the first time (The Super Mario Bros. Super Show!) that the Mario Bros. came to the Mushroom Kingdom. Koopa then tells Kooky to retreat, and jumps down a pipe. Before Kooky can follow, Raccoon Luigi hits him with his tail, knocking him into the air and into the pipe.
Aftewards, Princess Toadstool congratulates Mario and Luigi. She commented that King Koopa should have never tried to mess with history. Mario comments that Koopa also should not mess with himself and Luigi, and Luigi remarks that maybe next time, Koopa will try to pick on someone his own size. Mario and Luigi then put their arms around each other's shoulders, and give their thumbs up.
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