SMG4: Stupid Mario Maker 2 is the sixteenth episode of Season 9 and the five hundred and sixth overall to be uploaded by SMG4.
This episode was aired on June 29, 2019, just a day after the release of Super Mario Maker 2.
The episode starts in Peach's Castle with Mario happily humming while standing in the corner. When Princess Peach asks Mario what he is doing, he says that he is playing with his "salami". Believing him, Peach says that she is going out and tells Mario not to break anything while she's gone. Mario responds with a thumbs-up, but Peach suspiciously stares at him due to previous incidents, causing the plumber to sweat. As Peach finally leaves, Mario faints. It is revealed that Mario actually was holding onto the Nintendo Switch with Super Mario Maker on it from R64: Stupid Mario Maker and was playing on it, saying that he can make whatever he wants. As such, he summons many Spaghetti related objects before creating a giant dish of spaghetti and jumping into it. As Mario swims, he doesn't realize he is scrolling through objects on the Switch (Creepy Peach and Baldi to be exact) before ending on the words "Delete Level" and pushing the option.
This causes Peach's castle to completely de-spawn as Mario and any other Toads in the castle at that moment to plummet towards the ground. Luigi soon rushes over towards his brother and asks what just happened; Mario's response is hiding the Switch behind his back and saying that he doesn't know. Luigi then suspiciously asks his brother if he was playing Super Mario Maker, to which Mario says that he wasn't, but Luigi sees right through the trick and says the game is cursed, telling his brother to give him the Switch to which he tells Luigi to leave the Switch alone.
Mario then says that all he has to do was hit the undo button, but it instead erases a nearby Toad. Fortunately, Mario has the option to return the Toad. However, the Mario Bros. soon panic when they bring the Toad back; they succeed, but the "Toad" had the body of a ? Block, the legs of a Bob-omb, and had several other Mario enemies jammed into his sides.
As he runs off, the shocked brothers agree on asking the Toads for help on repairing the castle. As the Toads begin repairs on Peach's castle, Taskmaster Toad asks Mario how should they go at building the foundations. Mario begins typing intense codes into the Switch and summons several MTL crates. They, however, crush a Toad and knock a crane over, setting the foundations on fire along with the Toads working on it. Taskmaster Toad then asks Luigi to help his brother. Luigi offers Mario help, but he refuses, saying he got it. Luigi then said it'll be fun like when they played with Lego blocks as kids. After a flashback with the brothers dancing with a LEGO Yoda, Mario agrees, saying it sounded like fun. Later, Luigi asks his brother for the Switch to which he responds by summoning a Thwomp to crush him. Not wanting to go down some stairs, Mario turns the stairs into slopes. However, he didn't notice that the "slopes" actually led to a part of the floor still under construction, which caused him to break the ground and fall into Hell (the Nether from Minecraft).
Afterward, Luigi was placing some brick blocks to complete the castle while Mario scrolled through some fan art. Noticing Luigi's task, the plumber decided to prank his brother with some art that portrayed him in a negative way. This led to Luigi getting steamrolled after Mario left an image of him pointing a gun at a Toad; some Toads came by and thought that Luigi was enjoying the thought of shooting him.
In the main hall of the partially-completed castle, Luigi was using his Switch to install some safety barriers for the rooms that weren't finished yet. Meanwhile, Mario continued to goof around by spawning objects that didn't help with the construction at all. Once Luigi leaves to take a break, Mario realizes his opportunity to play around with the Switch and chooses to download a bunch of levels to the castle (which appear as randomly placed doors).
When Luigi returned and discovered the misplaced doors, he immediately told Mario to stop with what he's doing. His brother reassured that everything's fine, only to find the Angry Sun charging towards them upon opening one of the "doors." Thinking that the mess may be too big for them to undo, Luigi decides to just abandon the castle and re-do the entire project. Unfortunately, Mario has managed to block the exit with three levels, forcing the two to find another way out of their current situation.
Mario then proceeds to open some more doors (with various weird characters and scenes inside), but had no luck. After some time, the messed-up Toad from earlier emerges through one of the doors and takes the Nintendo Switch from them for himself, shortly before going into one of the levels that Mario had downloaded. Forced to chase him so they could leave the castle, Mario and Luigi chose to follow suit and go into the level as well.
In the first level that the brothers encountered, there were simply a bunch of randomly placed enemies before the Warp Pipe that the Toad disappeared into. Mario makes it through the first batch of enemies with ease, but Luigi realizes that their opponent has messed up the levels after witnessing Shrek pop out of an item box. Mario initially isn't sure what Luigi is talking about, even when one of the cannons sends out a TF2 character with the intention of torturing him. This ends up scaring Luigi to the point where he's able to outrun the remaining enemies in the level and jump into the Warp Pipe at the very end.
After emerging in the next level, Luigi finds out that he doesn't really have many obstacles to deal with. He quickly makes it to the pipe at the very end, just as Mario emerges in a car with the enemies from the previous level (all defeated). Mario spots a giant coin and wants to collect it, but is forced to follow Luigi without it because of the Angry Sun.
Beyond the near-death encounter with the burning, raging star, Mario and Luigi end up in an upside-down level where gravity happens to be reversed. Mario had a plan to overcome the level, which is by simply turning his head right-side up (against the gravity). But by doing so, he ends up breaking his neck and falling upwards onto the level's platform.
Many levels later, Mario and Luigi end up in a stage with a clear condition: Bring the toad to the end. Luigi asks Mario if he still has the Toad with them, and Mario answers that their subject is fine (even though he was dragged into some lava by the plumber).
At the final level, Mario and Luigi find that the stage is extremely difficult with a bunch of lava, randomly placed buzzsaws, a tower of Bowsers, and even a giant cannon before the mutated Toad at the very end. To prove his ability, Mario kicks Luigi onto an adjacent platform. However, the nearby cannon ends up hitting him with a Koopa Troopa, causing the scared brother of Mario to lose a life and respawn with a high doubt about completing the level. Realizing that his previous idea didn't work, Mario decides to run through the level himself by thinking of something that he hates - Toad puns. This results in the enraged plumber passing the obstacles with ease until he reaches the giant cannon, which shoots a Banzai Bill that homes in on its target.
Initially, it seems as if the Banzai Bill would allow the Toad to be successful. But at the last minute, Mario goes under the stage and hangs onto the cloud beneath the Toad, who gets hit by the Banzai Bill instead. An explosion rocks the stage as the Toad is seemingly defeated, with the Mario Brothers returning to their usual setting in the Mushroom Kingdom.
Now back home, Luigi congratulates Mario while he's still on fire with the Nintendo Switch in his hands. However, their victory is short-lived as they witness an angry Princess Peach, having returned to find her castle missing (or likely messed up, but the exterior wasn't seen in the video). Mario starts to blame his brother for getting them into trouble in the first place, while Peach takes (and probably confiscates) the Switch and uses it to download a new castle for her to live in. In the end, the unhappy princess spawns an Angry Sun in the Mushroom Kingdom to burn the Mario Brothers, as punishment for their actions from earlier.