SMG4: Stupid Mario 3D World is the eighth episode of Season 9 and the four hundred and eighty-three overall to be uploaded by SMG4.
This is also the 17th episode of the Stupid Mario series where several Super Mario 3D World characters, including Plessie, Green Sprixie, and Hisstocrat, make their debut. It was aired on March 9, 2019.
The episode starts out with Mario, Luigi, Toad, and Peach Toadstool, who was long absent up until now, watching the fireworks over the castle. While everyone praised the fireworks, Toad unsurprisingly wanted to use them to destroy the castle due to his hateful nature and his bad past with Peach, Mario, etc. Mario suddenly got hungry while watching and ordered Toad to get him some spaghetti. When Toad refused, Mario told Peach to make him a sandwich. Due to her bossy demeanor, Peach slapped him far onto somewhere near a clear glass pipe in response. The others came to check it out, and Peach told Mario to fix it. The unwilling Mario mocked her for being demanding, only to get kicked by her. Mario then hit the glass pipe with a toy hammer once, fixing it. The pipe then made many items (including a Furret) spew out of it. One of these things happened to be a Sprixie Princess, begging the gang to protect her from someone trying to capture her.
Instead of helping, Mario put her in a jar thinking she was a leprechaun who could grant wishes, with Toad correcting him that leprechauns give gold and not wishes, though he tried to force her to give them her gold. Suddenly, Bowser popped up and captured her anyway, claiming that it was Bowser Jr.'s birthday and he wanted to get him a dancing leprechaun. With the Sprixie now captured, Peach forced everyone to go out and rescue her, much to Mario and Toad's shared chagrin since Bowser was only doing it for his son, with Luigi following along.
The pipe took them to the Sprixie kingdom, but unlike the original, the place was a ghetto, overflowing with crime and corruption. While roaming through the city, Mario found a Super Bell, but was advised by Toad not to take it, since it transforms the user into a cat. Mario later managed to find a pipe while racing a Yoshi, and it took them to a hill. To Mario's dismay, the gang had to get past a giant gap between them and a bridge. Peach glided over the gap, Mario kicked Toad to the other side, and Luigi scuttle jumped his way through the gap. Unfortunately, Mario ended up falling into the river, and the current kept pushing him away. The currents were so strong, it ripped Mario's arm off (though it came back). Just when it seemed to be the end for him, Plessie saved him and took him to the other side to Toad's dismay.
The gang then found another glass pipe, which took them to a cloud level. Mario was so mad at this point that he punched a Biddybud in the face and shot Hisstocrat with a cannon he found (with Toad commenting that he likes Mario when he's angry), who gave him a Double Cherry. When he ate it, it created an exact duplicate of him. Mario started to get happy with his clone (unintentionally insulting Luigi and forgetting about his existence), and the two went and annoyed Toad. Bowser then showed up in his car, with Peach noticing him. The gang fought him with Luigi punching Bowser, Peach throwing Toad, and the two Marios ground pound his face (much to Bowser's surprise, as he assumed that there would be only one Mario). Having enough, Bowser used a Super Bell on himself to turn into Meowser (with Mario accusing him of being gay) and shot a fireball at one of the Marios, only for the other Mario to jump in front of it to sacrifice himself for the first Mario. Wanting to avenge his late clone, an angry Mario went after Meowser alone, using the Super Bell. However, instead of giving him a suit, it instead turned him into an actual cat, but nonetheless gave its powers.
Mario then found Meowser on a Skyscraper, and the Koopa King started climbing it, with Mario following suit. However, Meowser used his fire breath, forcing Mario to use a Pianta as a shield. Meowser then used a Double Cherry and created four clones of himself, but Toad, using the Koopa Clown Car, shot them down, and cornered Meowser, allowing Mario to kick him in the penis. With the Sprixie rescued, Mario celebrated, but the Sprixie ruined his celebration by saying that Bowser kidnapped 6 other Sprixies. Not wanting to do everything all over again, Mario just sold her to a merchant (to the dismay of Peach and the others).