Midbus is a brawny, unintelligent, pig-like creature and a major antagonist in Mario & Luigi: Bowser's Inside Story, acting as Fawful's chief minion. Akin to his master's tendency to speak in Engrish, Midbus speaks in broken sentences and gives unnecessarily long names to various weapons that he uses (for example, he refers to Junker as "Super Ultra Great Mega Trashy Monster Junker Bot"). His name is a pun on the phrase "mid boss", and he himself is fought by Bowser three times during the course of the game (the third time as Blizzard Midbus, his powered-up form). Just as Bowser is a cross between an ox and a turtle, Midbus appears to be a combination of a boar and an armadillo, although he also has a pair of bull horns like Bowser in addition to his tusks, and is similar to him in build and temperament, making him a foil as well as a rival to the Koopa King.
When Bowser meets Fawful, he sends Midbus to battle him. During the battle, Fawful unintentionally teaches Bowser how to use his action commands on Midbus. Due to the effects of the Vacuum Mushroom, Bowser ended up getting weakened, and Midbus and Fawful abandon him, but not before telling him that they plan to take over his castle.
Later in the game, Fawful puts him in charge of Bowser's Castle, his now secondary base, along with Bowser's now brainwashed minions. When Bowser approaches the castle, Midbus makes it animate to attack him, as he lands the castle on top of him. Bowser then becomes giant thanks to Mario and Luigi. Midbus fights Giant Bowser within his own castle. After being defeated, he accuses Bowser of cheating before retreating with the castle into a new area. He later drops an enormous iron ball on Bowser, but he is able to toss it back, preventing the castle from moving any further.
When Bowser reaches the castle, he realizes it's been completely changed by Fawful. Bowser finds out that he made a piece of Bowser's castle into a gigantic auditorium with a big stage at the end of it. Fawful is seen hosting some kind of show or act. When Bowser is about to fight Fawful, he sends Midbus to battle him again in a cage match.
In this battle, Midbus attacks in various ways. One of Midbus' most prominent moves is his body slam move (which he also did at the beginning of the game in the tutorial). He'll bounce three times on his belly, then jump into the air either directly above Bowser or a little to the side. If the former, Bowser must press so that Midbus will land on his spiky shell rather than his head. If the latter, he must punch Midbus away or make Midbus land on his arm or risk getting hit by the shockwave from Midbus' body slam. This move can Confuse Bowser or flip him over for the latter. He can also go off-screen and grab a wrecking ball and return while swinging it rapidly. As Midbus approaches Bowser, he must duck and hold Y for three seconds, then Midbus will spin back, but before he stops, he'll either have the wrecking ball raised up high or down low. If it is up high, Bowser must duck the attack, and if it's down low, Bowser must punch it away. This move can confuse the player. His last move is sucking up all his energy and then walking forward for a giant punch. Bowser must rapidly punch his belly to cancel his attack. He can also counter the second Midbus grabs his belly in pain, and hurt him with a punch. This move can flip Bowser on his shell. If he executes any of his moves correctly on Bowser, the Audience will throw him Coins (which are useless) and Food which Midbus will eat to heal. The doughnuts heal 10 HP, the cakes heal 20 HP, and the meat heals 50 HP. Bowser can Inhale the food to use himself which will do the exact thing, but meat makes his Attack go up and heal 50 HP as well. If Bowser makes any of his moves excellent, Bowser will only receive 10 coins. After Bowser finally defeats Midbus, he is rewarded with a banquet feast. He gets overstuffed though and gets stuck in the floor shortly.
Later in the game, Fawful and Midbus see Bowser stuck. Midbus then watches as Fawful begins to use a ray gun, the reason for doing so being to find the princess for part of his plan. He then increases the power on the ray, and eventually finds the princess. Fawful then stops firing the ray as a light emerges from Bowser's body, and the princess emerges on Fawful's shoulder. Midbus brings out a treadmill, which Bowser falls onto and uses to make himself normal-sized again. Before Bowser can fall on, though, the pair leaves, with Midbus ignoring Fawful's orders to help him carry the princess.
In Princess Peach's Castle, Mario, Luigi and Starlow meet the pig for the first (and so far only) time. Midbus makes a trash monster attack the Mario Bros. so they can't pass to rescue Bowser who is knocked out. After the defeat, he goes into another area of Princess Peach's Castle.
Later in Peach's Castle, Bowser meets Midbus again. Fawful powers Midbus up, and he becomes Blizzard Midbus, whom Bowser must fight to progress through his adventure. After Midbus is defeated for the third and final time, he gets frozen in an ice cube and starts spraying frozen mist from his nostrils. Bowser inhales this mist due to pain in his chest (owing to the Dark Star eating his DNA). The mist goes up the Airway, Mario's next destination. Mario, Luigi, and Starlow must use this frozen environment to their advantage to get to the Dark Star. Midbus supposedly got free from his ice block due to Dark Bowser's storm before Bowser fights with him.
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