SMG4: Mario and The Diss Track is the fifty-fourth episode of Season 8 and the four hundred and sixty-second overall to be uploaded by SMG4.
The episode starts off with the Mario Brothers getting kicked out of a restaurant after Mario was caught playing with the food. As Luigi started lecturing Mario for his disgusting behavior, they noticed that Bob has become immensely famous, and there were shirts, balloons, and posters bearing Bob's name. Deducing that Bob would do something awful to them, Luigi decided to go to the castle, but not before Mario stole another guy's balloons and floated away until he hit a random airplane advertising Bob.
Meanwhile, Bob was at a huge mansion thanks to his overwhelming popularity with Fishy Boopkins' former girlfriend, Saiko Bichitaru as his manager. He was annoyed at how his follower count has not risen up in days, and Saiko revealed that the reason was that everyone in the Mushroom Kingdom became his follower. However, the Garo did not care at all and explained that he wanted everyone in the world to know his name. Saiko suggested threatening them and although Bob said it was not his idea, he nevertheless accepted.
At Peach's Castle, everyone was doing their usual hobbies, until Luigi burst through the door carrying awful news. Toad, being the hateful wiener he is, happily asked if Mario died, only for the latter to show up carrying Bob's stuff, much to his frustration. Luigi explained that Bob had skyrocketed to fame, but the others (except Fishy Boopkins who fell off the couch upon remembering himself ruining Bob's concert) thought he was just jealous of the Garo's success, with SMG4 assuming Luigi knew nothing about fame. But when they decide to watch one of his concerts on TV, however, Luigi's fears were confirmed when the concert, called the Ultimate Diss Track, showed nothing more than Bob hurling hurtful insults at his former friends (criticizing Mario for his pasta obsession, pointing out how Luigi is manipulatable, calls Meggy an annoying squid girl with a screeching metal voice, says Tari's obsession with video games obnoxious, calls Toad and Bowser a waste of space, SMG4 an unfunny disgrace, and Boopkins an anime-loving green turd), claiming they made his life miserable and ended the rap by lying that it was all true. Mario was not concerned at first, happy that they were at least on TV, but the others were deeply offended, horrified, and angry at Bob for humiliating them. Luigi then decided to tell the gang all about the cruel things that Bob did.
Meanwhile, Bob was at the studio where he made his concert and was happy at how popular it would become, though he was somewhat sad that this cost all of his friends, but stated it was "totally" worth it. Saiko was happy, believing everything Bob said was just a joke and left the studio, planning to start her own singing career. While exiting, she found a Mario-esque shadow. Naturally panicking, she threw her phone at it, discovering it was just Luigi. He revealed to Saiko that Bob indeed hated them and manipulated her just to get more fame. She refused to believe it at first, but Luigi showed her what happened to Fishy Boopkins, who was shaking uncontrollably in sadness and was starting to lose his sanity after Bob insulted him. Seeing what Bob did to her former boyfriend, Saiko agreed to join Luigi.
Back at the castle, the gang was formulating a plan to get revenge on Bob. Mario suggested slugging him with a baseball bat which Toad agreed on while Tari suggested a less-violent idea involving them challenging Bob to a video game competition. However, Mario and Toad instead laughed at her idea while Meggy showed disinterest. Luigi then came back with Saiko, who was angry at Bob for manipulating her and for what she did to Boopkins but was unable to say the word "friend" at first (although she eventually did, which relieved him). Luigi was about to give her a pat on the back, but she proceeded to crush his hand in retribution, wanting her personal space. When the gang welcomed her, Saiko suggested an idea in order to teach Bob a lesson he would not forget.
Back at his mansion, Bob looked at the TV and was surprised that his follower count had risen up. He proceeded to see any possible rival, and discovered a rap called Darkest Hour, where Saiko was the singer, Mario was the drummer, SMG4 and Meggy were the guitarists, and Luigi, Tari, Bowser, Boopkins, and Toad helped film and set up the rap. Their song (which revealed all about Bob's cruel acts) did so good that Bob lost his fame and all of his fans to Saiko, plus they ditched their Bob Merch and did not want to listen to his raps anymore (with the chef who kicked the Mario Brothers out of his restaurant at the beginning yelling at Bob to stop).
To make things worse, Bob lost his mansion, since Saiko paid for it, and though he tackled and defeated the Teletubbies responsible for getting rid of his house, another Teletubby grabbed it with its bare hands and left with it. Realizing his fame and life had been destroyed beyond repair, Bob saw his friends inside a store and attempted to reconnect with them, only for them to shrug him off and turn back on him on retribution for humiliating them all. Bob then asked Boopkins who came out if he would at least be his friend again, but Boopkins simply looked on sad before going back inside, which was enough to tell Bob that his answer was no, leaving the miserable Garo distraught.
In the credits, Saiko (or her singing voice actress, Ellyn Barclay) advertised to the viewers that Darkest Hour was available on Spotify and iTunes.
Note: All below are used as fans of Bob and later on Saiko.