Koopa Command Center

From the Super Mario Wiki

The Koopa Command Center, also called the Koopa Headquarters, is a fort held by Iggy Koopa in Brain Drain. Iggy uses it a base of operations while he is mind swapping people using his Synapse Switcher, which is also located within the Command Center. Luigi ends up in its control room after having his mind swapped with that of a rank-and-file Koopa Troopa. As soon as he arrives, he is ordered by Iggy to return to his post, which involves turning on the Synapse Switcher. Luigi then wanders off in search of clues on how to reverse the Synapse Switcher, spotting both a room marked "Top Secret" and a room marked "Cafeteria". As the secret room is only a small closet with cleaning supplies, which is completely useless for Luigi, the correct choice is the cafeteria, where Luigi can satisfy his appetite. The cafeteria is serving platters of unappealing slop, and Luigi wonders if he should use the nearby phone to call in a pizza. If he goes with the slop, he orders a platter of gray gunk and finds that it actually tastes good. If Luigi uses the phone, a "Koopa code" must be inputted first, which is partially scrawled on a nearby wall (which the player must solve in a puzzle; the code is "13572468", and getting it wrong lands Luigi in a dungeon with a Game Over). After ordering a pizza, a Pidgit flies up to an open window and delivers the pizza to him, although he saves the pizza for later when he finds that the Pizza tastes bad to him.

Regardless of where Luigi ends up, the fort is eventually stormed by Mario brandishing a Fire Flower. Luigi runs ahead of the other Koopas to reconvene with Mario, although Mario first asks Luigi for the Plumber's Oath that they had memorized previously (getting it wrong causes Mario to destroy the Synapse Switcher, permanently trapping Luigi in the Koopa Troopa's body and resulting in a Game Over). Once Luigi correctly says the Plumber's Oath, the two brothers storm the fort together, and the other Koopas retreat to WMUSH with the Synapse Switcher. The two of them leave the Command Center in search of any tracks that the Koopas left behind.