SMG4: Mario's Inside Story is the eleventh episode of Season 10 and the five hundred and sixty-fourth overall to be uploaded by SMG4.
This episode was aired on March 28, 2020.
Mario ate some bad spaghetti...
The episode begins with SMG4 creating a meme robot based on Carl Wheezer from Jimmy Neutron. As he was complimenting his "masterpiece", Luigi burst into the room with a sick Mario in tow, destroying Carl Wheezer. As Mario stated, he was about to take a poop in the basement bathroom when he found spoiled spaghetti, which according to Luigi, was probably there for the past 10 years. Due to his gluttony and stupidity, Mario unsurprisingly did not listen to Luigi and ate it, which resulted in food poisoning. SMG4, annoyed at Mario's gluttony, grabbed Saiko Bichitaru from the foyer and told her and Luigi to go inside Mario's body and fix the disease. Using E. Gadd's shrink ray, he shrunk Luigi and Saiko (causing her to believe SMG4 turned her ugly), put them inside a capsule, and had Mario swallow it.
The two ended up inside Mario's stomach, which was filled to the brim with spaghetti plates, Spy, Tinky Winky, Eggman Football and a can of bleach, causing Saiko to criticize Mario for his eating habits. They discovered the virus that was causing Mario pain and taking the shape of Mario, evading their attempts to capture it. The virus then created a hammer and smashed the stomach, forcing Mario to digest everything inside. Saiko was forced to grab a piece of spaghetti, wrap it around Luigi as if it was a rope, and flung it towards the blood vessel the virus went through. However, the virus managed to deflect Luigi and with the inertia from the flinging, they ended up in a different blood vessel. There, Luigi and Saiko discovered several Mario Cells who help keep Mario's vital organs in state. They initially mistook Luigi and Saiko as a threat but calmed down after Luigi revealed he knew Mario (through a picture on his iPhone which showed him and his brother, who was streaking in a mall, being chased by Hal Monitor), and welcomed them in. Inside Mario's organs, Saiko was disturbed upon learning that the Mario Cells worshiped Mario as some sort of god, even more than seeing him hump food naked.
Understanding the situation upon being asked where did the virus go, the cells formed up a ladder for Luigi and Saiko to climb up, getting them inside the area where Mario's brain rested. The brain was revealed to be smoking and mostly small (hence Mario's stupidity). The virus once again appeared and proceeded to enlarge, overpowering Saiko. Luigi begged Mario's brain for help, promising 10 plates of spaghetti with mayonnaise, 1 truck of vanilla ice cream, and Old Man Walker. The brain happily took the offer and killed the virus easily with a baseball bat, minigun and bazooka. This resulted in Mario cured. SMG4 was happy that Mario was cured, but when asked how would they escape, he revealed it was complicated. Mario then revealed he was going to take a poop in the bathroom, and both Saiko and Luigi, realizing they would be get out of Mario's body by his anal, screamed loudly in panic.