SMG4: The Mario Convention! is the forty-second episode of Season 8 and the four hundred and thirty-sixth overall to be uploaded by SMG4.
This episode was aired on September 22, 2018.
The episode begins with Toad putting his clothes in a bucket just to wash his clothes until suddenly the Merch Fairy (aka SMG4) makes a surprise appearance by throwing out Toad's clothes to promote SMG4 merchandise and also triggering Fishy Boopkins by calling a shirt with him on it crappy.
The actual part of the video begins with a convention (seemingly for everything) full of posters, crowds, and booths; including a sci-fi booth, a How to Oof booth and even a Looking for GF booth.
After a zoom out, Luigi appears cosplaying Finn from Adventure Time. Luigi was amazed by everything in the convention, but Mario thought everyone was a weirdo and was unimpressed, therefore asking if he could go home. Luigi tried to convince Mario that conventions were "fun", but Mario wasn't having it, and said that he was "outta here". Luigi desperately tried to get Mario to stay by saying that there was "something for everyone". Intrigued, Mario asked if there was a "Spaghetti appreciation booth" here, and Luigi told him there might be. Luigi then told Mario to come with him too. Mario was still unimpressed, but he half-heartedly agreed to go with him. They first went to a Sci-Fi booth, of which Bowser was running it with a Darth Vader helmet on. Mario was not intimidated (probably due to his bad mood) and thought Bowser was dressed as a Pokémon.
Bowser insisted that he was not, and Luigi and Mario started looking at the stuff Bowser had in his booth. Then, Luigi found a replica TARDIS (Time And Relative Dimension In Space) outside the booth. Mario asked Luigi what he had called him, confusing the word TARDIS for another name for retard. However, Luigi stepped into the TARDIS and pretended to be the Doctor from Doctor Who, when suddenly, the TARDIS de-materialized with Luigi inside it. Mario, unconcerned, then found a lightsaber, although he didn't know what it was. He began tossing it around despite Bowser saying that it was a real lightsaber, inadvertently activating it and making the blade go through Bowser's hand. Bowser stared at the blade for a few seconds before yelling in pain, much to Mario's amusement. Elsewhere, the TARDIS re-materialized a few feet away from the booth, with Luigi walking out of it. All this happened as Tari and Meggy passed by them.
Tari, cosplaying as Link, gasped in amazement at all the booths at the convention, while Meggy was following her, uninterested and weirded out by a Goomba and a Monty Mole cosplaying as Inklings. Just then, Fishy Boopkins noticed the duo and welcomed them to his Anime Store. Meggy, having had past recollections of all the horrors she experienced watching anime, tried to turn to leave, but Tari rushed past her and looked at everything in the store, much to Meggy's disbelief. Meanwhile, Luigi and Mario were walking away from the Sci-Fi booth where the latter questioned the convention's excitement. Just then, he spotted SMG4 going around a corner and happily went to join him. SMG4, seeing the brothers, welcomed them to his Tabletop Gaming Paradise!!!! which was empty except for a lone Birdo in the corner. As Mario turned to leave, Luigi asked if they could play Warhammer 40K, much to Mario's disbelief, and SMG4 happily set them up to play.
Meanwhile, Meggy and Tari came across a basketball hoop where the latter shot three times. Unfortunately, Tari's three shots only managed to hit the backboard, barely missed the rim, and hit a Spider-Man doll next to the hoop, of which the latter exploded when it hit the ground. After Meggy showed her how to throw the ball, a determined Tari threw the fourth shot, but it deflected off the rim and slammed Meggy in the face. After Meggy reassured Tari that she was fine, Tari noticed a huge crowd gathered around Hideo Kojima, the creator of the Metal Gear Solid series. Tari asked Meggy to bring Mr. Kojima to her, which she accepted.
Meanwhile, Luigi and Mario have finished playing and headed to the celebrity meet-up. Then, Luigi noticed Hideo Kojima and begged Mario to get him an autograph. Although Mario went to sleep due to being uninterested, he happily accepted when Luigi promised that they would look for the Spaghetti Appreciation booth.
At the meet-up, while Meggy was jumping from person to person, Mario rammed through the crowd with his kart. They both arrived in front of Mr. Kojima at the same time. Realizing that only one of them could talk to Mr. Kojima at the time, they started pulling at him while Tari watched from the side. Even though Tari wanted to meet Kojima, she suddenly got distracted from the meet-up by "something". Back at the meet-up, Mario won the tug of war and asked Kojima to come with him to Luigi. Suddenly, Kojima held a purple mushroom in front of Mario's face, and the Shroom started to glow. Realizing what was about to happen, Meggy knocked Mario out of the way a second before the Shroom exploded, sending the convention-goers into a panic while Meggy and part of the crowd became T-Pose Zombies, much to Mario's disbelief.
Kojima then revealed himself as Waluigi in his WaluRambo form and cackled evilly. Mario tried throwing a 1-Up Mushroom at Meggy, but it failed and bounced off the Inkling. Waluigi laughed and said that there was no cure to being T-Posed, as his powers have grown stronger ever since the events of SMG4: Mario SAW. He then threw a bolt of purple lightning at Mario, but Luigi tackled him out of the way just in time. Despite Mario's protests, Luigi pulled him away from Meggy so the two could leave the convention immediately, joined by Boopkins and SMG4, while various characters including Bowser, Shroomy, and a random booth owner became T-Pose Zombies from Waluigi's lightning bolts. As they neared the exit, Waluigi noticed them and threw a bolt at the group. While the rest managed to avoid the bolt, Luigi got hit and was transformed into a T-Pose Zombie. Mario, in tears, promised his brother and Meggy that he would come back for them as he ran away from the destroyed convention with SMG4 and Boopkins.
When night fell, Tari emerged from a bin full of toys, having found a rare wizard duck that happened to be what distracted her earlier. As she walked around looking for Meggy, Tari heard Waluigi's laugh and saw him above his army of T-Pose Zombies. She was then shocked to see Meggy among the T-Posers, now obeying Waluigi and under his control. As Waluigi announced his plans to make the world feel the rejection he felt, Master Hand intervened, but when he tried to use Flying Punch on Waluigi, the madman stopped him effortlessly and tortured him until Master Hand pledged his servitude to him. Having taught Master Hand who was the "master," Waluigi laughed. The episode ends with a cliffhanger of a horrified Tari clutching her duck and crying in fear watching the scene unfold from behind the bin.