WMUSH is a radio station in Brain Drain. Its tagline is, "The station that tastes great in omelet!" It is being used by Iggy Koopa and his minions to transmit the Synapse Switcher's signals, causing anyone who listens to the radio station to have their minds swapped. It features a large neon sign at its entrance, and it is staffed with a variety of species, including Wigglers, Ninjis, Chargin' Chucks, and Urchins (inside of a fish tank). Iggy serves as the station's DJ, reading whichever song plays next at the Synapse Switcher's control panel. It is first mentioned while Mario and Luigi are fixing the Mushroom King's soda machine: a nearby radio is tuned into WMUSH, and it advertises Fungus Up. Later, Luigi arrives at the station in the body of a Koopa Troopa. Iggy orders him to retrieve a tape with his music video from the recording studio. The studio contains a VCR and a TV with a stack of videotapes next to them, as well as a computer with a nearby floppy disk that reads, "Iggy's Disk." Luigi guesses that one of the tapes, labeled "MC Koopa: The Music Video," is what Iggy was looking for, but he wonders if he should watch the tape or examine the disk. The choice requires the reader to solve the puzzle, though either path is valid.
If Luigi goes to the television, he surmises that it must be important if Iggy wanted it, and starts to watch the music video. The video features "weird" Koopa music, with Iggy dancing while dressed in a gold jumpsuit and a green wig. As he is in a Koopa's body, he starts to get into the music, and he feels his body starting to dance. However, as he hates absolutely everything about Koopas, he might become mortified if he starts dancing to Koopa music. He then has the choice of either bolting out of the door or continuing watching TV (which involves solving another puzzle). Although both are presented as valid choices, continuing to watch TV gives a vital clue. If Luigi continues watching, he finds himself enjoying the music, and starts to dance in a rhythmic pattern. After dancing for a while, he realizes that he is dancing in a loop, and that his footwork corresponds to a series of letters on the floor. His dance corresponds to a message, and finding the message involves the reader solving another puzzle. Luigi's dance is the "Koopa Cotillion," which involves three distinct parts repeated three times: two steps forward, one step to the left and two steps forward, and two steps right and three steps back. Following this pattern reveals the message to be "A FUNGUS UP", referring to how Fungus Up is the cure for mind swapping. If Luigi runs for the door, he mutters to himself that he could never face the others if he danced to an Iggy Koopa video.
Afterwards, an alarm suddenly plays out, warning that Mario and Luigi (who is actually Princess Peach) are approaching WMUSH. Iggy points the Synapse Switcher in their direction in an attempt to send their minds far away from the station. He boasts that they can never be cured afterwards, as the only cure is sitting on the table besides him. The table holds two different drinks: Fungus Up and Morel Moxie. Luigi immediately grabs both of them and runs outside to meet with the others. As he does not know which drink is the cure, he randomly picks one of them to drink (although the choice is given to the reader). If Luigi drinks the Morel Moxie, his mind ends up swapped with that of a pony, leading to a Game Over.
If Luigi goes to the computer, the screen presents him with two option: "Synapse Switcher" and "Games". To decide which to choose, a crossword puzzle must be solved, with the remaining letters indicating what should be done. The letters, when read from top to bottom, spell out "PLAY SOME GAMES." If Luigi attempts to examine the Synapse Switcher file anyways, he finds that he cannot understand the file's language and accidentally deletes its contents. He sighs before taking the music video to Iggy. If he plays some games, he boots up a game featuring him and Mario called Pound the Plumbers. Annoyed, he goes to turn it off, but a message then appears, saying that the code for reversing the mind swapping is gained by reaching the game's highest score. Although the high score is thirteen, it is not relevant until another puzzle uses it as its key. He then goes to deliver the video.
Afterwards, Luigi returns to the control room, where Iggy is mad at him for taking so long. Luigi asks about the tape's contents, and Iggy replies that the music video's song, "Anchovies with Extra Cheese" by The Pizzas, holds the secret to the Synapse Switcher (and not the video itself, despite containing a code if Luigi had watched). He then orders Luigi to monitor the Synapse Switcher while he goes to watch the video. As Iggy walks away, Luigi suddenly remembers that he had a Tape of the same song in his toolbox, though whether he brought it or left it behind depends on the reader's prior actions. If Luigi does not have the Tape, he attempts to ask a nearby Sumo Bro for a copy of the tape, and he is promptly thrown in dungeon for revealing that his mind was swapped, as Iggy had ordered all copies of the Tape to be destroyed; this results in a Game Over. If he has the tape, he uses the Synapse Switcher's built-in tape player to listen to it. He notices that the chorus contains a voice reading a string of letters ("VBIILT YRQQLK"), and realizes that he needs a key to break the code. The key, in this case, is the last digit of Pound the Plumber's high score, and applying that to the code reveals it to say "YELLOW BUTTON". If Luigi then decides to press the Synapse Switcher's orange button, it self-destructs, leading to a Game Over. If he presses the yellow button, a can of Fungus Up pops out of the machine. He guesses that Fungus Up is the cure and takes enough cans for him and his friends. He then runs out of the station while carrying the cans, with Iggy Koopa and his minions chasing after him. He ends up meeting Mario, who is also in the body of a Koopa Troopa, and they both drink a can of Fungus Up.
Once Luigi cures himself, he finds himself back in his old body, albeit with Peach in his original Koopa body. He soon gives the Fungus Up to the rest of his group, which includes Mario, Princess Peach, Toad, and the Mushroom King, and all of them return to their bodies. Everyone runs back to WMUSH to take care of the remaining enemies, but they only find a lone Wiggler attempting to drink a can of Fungus Up. The Wiggler claims to be Iggy Koopa, and Yoshi is meanwhile in Iggy's body. The group decides to leave Iggy in the Wiggler's body, at least for a while, and they all share a laugh as they leave.