SMG4: Sans's First Day In Smash Bros is the thirty-fourth episode of Season 9 and the five hundred and twenty-sixth overall to be uploaded by SMG4.
This episode was aired on September 14, 2019.
Sans is now in Smash! Only he doesn't really want to be...
The video begins when Sans woke up and realized himself that he was in Super Smash Bros. instead of the bathroom, along with Mario, Link, and Banjo and Kazooie. As the three fighters duked it out, Sans teleported in a beach chair and popcorn to enjoy the carnage. Suddenly, Banjo smashed Mario to near Sans where the plumber saw Sans. Mario remembered Sans but claimed he was from Earthbound. Sans told him he no longer held a grudge on him.
Just then, Banjo blasted Link off the stage, eliminating him. Sans had an idea involving such an exit. He picked Mario and threw both of them off the stage, causing Banjo to celebrate his victory.
Later on in the Smash waiting lobby, Sans looked around, seeing Banjo and Toad making some music and the very injured Link who tried using a fairy to heal him just for Villager to catch it with his net (Link got very righteous furious and chased Villager just to fail miserably and get a Game Over). Mario then came near Sans being mad over what Sans did to him earlier, which Sans explained as a method of leaving the Smash game (but jokingly said that it was to see the joy in torturing Mario, understandably making Mario horrified). Mario, now understanding why Sans did what he did, was horrified of the possible consequences, stating that attempting to leave early without permission would incur the wrath of Master Hand and such attempts would never work as he made it mandatory for all to stay forever.
As Sans complained about how being in Smash was a lot of work, Mario agreed, saying he could have been eating spaghetti. The two then laid on the floor with Mario calling Sans the brother he never had, just for Luigi to just so happen walk by and feel heartbroken.
Suddenly, Master Hand came in and wanted people for his next match, horrifying everyone into running away. However, he then managed to grab Kirby, Lucinia, Solid Snake, and Wario. Just then, Sans exclaimed upon seeing Master Hand was a jerk and wanted to leave. Mario also considered but realized that Master Hand would attack his groin if he left. Just then, King K. Rool and Banjo got into an argument that ensues the whole place into Sudden Death.
As Mario took part in attacking the Ice Climbers, they quickly devastated him and would have killed him if it wasn't for Sans returning from the actual bathroom and using his Gaster Blaster (but claimed was from sneezing). As Sans wondered if Mario knew the way out, Mario said yes but initially was against it. However, the moment he saw Donkey Kong easily beat up Yoshi, Mario agreed.
In the backstage of the Smash stages, the pair were trying to get out. Opening random doors, Mario saw Pikachu beat up Pichu, Terry Crews with a Terry Bogard wig and Ridley and King Dedede beating up Luigi (Luigi wanted Mario to help him but Mario closed the door). As Mario kept searching for the exit, Master Hand appeared. Mario tried to come up with a reason but Sans just outright stated what they were doing, causing Master Hand to get mad. Stating that people trying to leave without permission would get a "SRS ASS whooping" and proved it by flattening Mario.
Sans then became prideful and asked for permission, which Master Hand angrily gave to him by flinging him through the wall. Sans landed outside but insulted him with a joke regarding a hand. Naturally, Master Hand became angrier and proceeded to beat up Sans although it did nothing much. Despite Mario pleading for Sans to apologize to Master Hand, Sans still kept his stubbornness until Papyrus showed up. Once that, Sans decided it was time to go and then showed Master Hand that he was holding back the entire time and gave such a brutal beatdown that Master Hand died from the attack.
As Sans and Papyrus drove off, Mario noticed that Banjo and Toad were behind him making such a song. It ends with him feeling horrified.