Mario is introduced to the game "the idiot test" and see if he's smart enough to pass it.
The video starts with Toad teasing Mario off-screen, saying "u mad bro?", which follows with Mario angrily roaring at Toad. Mario then goes into SMG4's room and rushes towards him. SMG4 turns around and is seen with a knife in hand and a bleeding Link on the floor. He states he wasn't doing anything, and Mario responds with another angry roar, confusing SMG4. Mario asks him where he put his gun, and the scene cuts away to outside the castle, where Baby Mario shoots Luigi with Mario's gun.
Back inside SMG4's room, Mario asks SMG4 what he's doing now. He tells Mario he's been playing an online game called The Idiot Test. Interested, Mario asks SMG4 if he can play the game, but he just bursts into laughter. Angered by this, Mario throws a knife at SMG4, but it instead hits Luigi through his head, who apparently just entered SMG4's room.
SMG4 tells Mario he doesn't even know what's 1 + 1 is, but Mario denies this. He tries to solve the problem in his head, but after several seconds without an answer, he insists that he can do the idiot test. Mario proclaims, "I'll show you I AM AN IDIOT!", with SMG4 replying to his shortsighted remark, saying "You just did."
Mario begins to play the game, which instructs him to press the square to begin the test (the game even gives Mario a hint that the square is blue). Mario feels confident that he knows what a square is, but he incorrectly chooses the yellow triangle instead. This dumb decision prompts Mario with a screen telling him to go back and try again with the BIG rewind button, but he somehow can't find it. Watching Mario fail horribly, SMG4 says it's no surprise that he can't even get past the game's introduction. On his second attempt, Mario does pass the first screen, but he does so by simply guessing the blue square was the correct choice.
The second screen tasks Mario with pressing the big red button to continue. This confuses Mario, as all five of the buttons on the screen are red buttons. SMG4 tells him to think, emphasizing the "BIG" in "big red button." Mario tries to concentrate, but he cannot seem to do so and instead envisions a Luigi dancing on the computer screen repeatedly chanting "Go Weegee!". Mario yells at the image to get out of his face, addressing him as Luigi. This causes the real Luigi to mistakenly believe Mario called for him, who ends up throwing a frying pan in his brother's face for some reason.
Mario seems to have the correct answer in mind, as his cursor his hovering over the largest red button on the screen. This makes SMG4 hopeful for his success, however, at the very last second, Mario moves the mouse over one of the smaller buttons and selects it, thinking that it is the true answer. This is not the case, as the idiot plumber is again greeted with the failure screen, causing him to furiously shout "Mama F**ker!" three times before throwing SMG4's computer (which somehow hits Luigi) out the castle window in a fit of rage.
SMG4 can only sigh in disappointment at Mario, who proceeds to visit lolcats.com, a different website. SMG4 tries to get Mario to continue taking the test so his intelligence can be determined, but Mario refuses out of fear that he will be humiliated. SMG4 tells him nobody will see him and to not worry, although this is a blatant lie as SMG4 is holding a camera as he says this to Mario.
Mario complies with SMG4 and resumes the idiot test, actually pressing the BIG red button because, as he puts it, "it represents my fatness." Mario advances to the third screen, which prompts him to click on the rectangle in order to proceed. Mario again becomes confused, but SMG4 reminds Mario to remember what he said. Mario tries to do so, but much to his dismay, he simply cannot, and instead thinks of several off-topic sayings from SMG4 that do not help him with the test. At this point, Mario has to guess the correct answer.
Just then, X shows up and asks SMG4 Mario is doing. SMG4 replies by saying, "Failing at the idiot test." Immediately following this, X swiftly ducks his head to avoid a frying pan thrown by Mario out of anger.
Mario then correctly guesses the solution to the third screen and clicks on the rectangle. Mario celebrates as he's presented with a screen that states he passed the first level of the test and can now consider himself as a borderline idiot. SMG4 reminds him that there's still more to the test, so Mario continues to level 2. The very first problem he is presented with is, "what is: 1+1?" Mario believes he his screwed, but SMG4 tries to encourage him to use his brain. Following SMG4's advice, Mario tries to use his tiny brain, as seen inside his head, but to no avail.
Mario then notices that the game has a hint for him. Thinking it might help him, Mario opens the hint, which reads, "its not spaghetti". Mario becomes so confused after reading this hint that his mind explodes.
Mario proceeds to have a seizure as he repeats a certain phrase before eventually catching on fire. SMG4 can only say "So sad..." at the sight of this. The end screen then appears, reading, "Oma sake de de de de de de de de" and, "translated: thanks for watching".