SMG4: Mario's Illegal Operation is the tenth episode of Season 9 and the four hundred and eighty-seventh overall to be uploaded by SMG4.
The video begins with SMG4 and Mario destroying the former's merchandise. Turns out the reason is to make way for the next season of merchandise in the shop and that all Season 1 shirts were 15% off until 30 March.
The actual video begins with the breaking news with Kermit The Frog stating that Anime is destroying the Mushroom Kingdom due to the events of SMG4: Mario and the Anime Challenge, with Steve acting like Red and riding a elephant which he names Pikachu, and Frankie tells Kermit that he kills people and he is holding the "Death Note". The city has been damaged by the Mushroom Kingdom community while Mario, Tari, Fishy Boopkins, and Bob, the ones who accidentally started everything, all watch in horror (excluding Mario, who as usual is acting retarded and Bob, who is bragging about his victory back the Anime Challenge). Furious over the destruction of her kingdom, Peach Toadstool declares anime a bad influence on the citizens and permanently bans it. A division that arrests people for owning the now illegal anime called Anime Secret Service (aka "A.S.S") is then established to destroy all remaining anime, with SMG4 as the second-in-command. Toadsworth also burnt some anime while saying "Why don’t you understand that anime belongs in the trash?".
In a garden, the Mario Bros. watch as a pile of anime body pillows start burning. Luigi complains to (and blames) Mario for destroying anime, only for the plumber to say that anime was dumb anyway. The brothers then see Fishy Boopkins trying to stop an A.S.S agent from burning his last anime body pillow, but he fails and starts crying. Luigi tries to comfort Boopkins, but Mario (as usual) does not care and refuses to help him, causing Luigi to punch him. The trio then sees Lemmy Koopa (one of the Koopalings and Boopkins' friends) and are persuaded into coming with him to an alley. Bob, who was waiting for them, then shows that he and Lemmy were illegally smuggling anime into the Mushroom Kingdom.
The group is then discovered by the A.S.S with SMG4 (Mario realized that A.S.S spelled "ass", causing him to laugh), who starts accusing his former friends of joining the "bad guys". He ignores Mario when the latter says that anime is what it is and orders their arrest, but focuses on Bob since he was holding a body pillow. Luckily, Bob is saved offscreen by his boss Francis while the others escape, but not before Lemmy tells Mario and Boopkins to help in smuggling anime. Luigi refuses to participate since that's illegal. Mario, on the other hand, sees this as an opportunity to make money, with Boopkins joining in after being promised unlimited anime. The trio then leaves Luigi behind, much to his dismay.
Mario and Boopkins are tasked with taking 4 crates of anime-related contraband to a warehouse but run into an A.S.S checkpoint. It shows its agents punishing people hoarding anime and they proceed to blow Hideo Kojima (the creator of Metal Gear Solid) and his truck up. Mario then gets the idea of disguising himself as an anime girl to distract the agents while Boopkins makes a run for it, and later takes off his clothes when cornered to show he was just pranking the agents. After arriving at the warehouse, the two then meet two masked men, who are actually Swagmaster and Chris in disguise. Unfortunately, Swag blows his cover as Mario recognizes his voice. As a last resort, Swag calls the A.S.S agents for an ambush, once again joined by SMG4, and blows up the crates holding anime with his rocket launcher.
SMG4 then tells Swag to stand down (as the latter wants revenge against Mario and Boopkins for getting him and Chris fired from being prison guards) and let him talk with his friends. SMG4 then tells Mario and Boopkins to surrender, but Mario responds by grabbing a doll, holding the Youtuber in a half-nelson and threatening to turn him into a weeaboo with the doll if not left alone. Despite having him outgunned, the A.S.S are forced to comply (though Swag wanted to kill SMG4 with his rocket launcher if it meant killing Mario), while Boopkins distracts them to make their escape. Swag and Chris then agreed to lie to Peach that SMG4 betrayed them and call it a day.
In the streets, Mario and Boopkins drop SMG4 off and start to panic, since Francis will kill them for losing his anime. They are then conveniently found by him and Bob in his limousine, with the latter showing his disappointment of Mario and Boopkins for failing. However, Francis is still convinced they will win, especially with SMG4 saying that he can help them since he worked for A.S.S, and has access to all of the security codes. They are given another chance, much to the delight of Boopkins. Their job is to escort someone out of the Mushroom Kingdom, then they are off the hook.
The gang then shows up at the airport, where they are joined by Saiko Bichitaru. Boopkins then asks her about why she's leaving from the Mushroom Kingdom, with the latter saying that since she is anime come to life, the A.S.S. will try to kill her. Saiko then said that they are going to Japan, which delights the gang. However, Francis demands Mario to stay behind because he needs him to make up for the money he lost. He then starts laughing maniacally, so much to the point where he can't breathe anymore and asks Mario for his inhaler.