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A Lost Luigi is the fifteenth episode of Season 3 and the one hundred and fourteenth overall to be uploaded by SMG4.
This episode was aired on March 3, 2013.
After being kicked out of the house, Luigi accidentally enters a warp pipe and is transported to another part of the Mushroom Kingdom. With the police hot on his tail, Luigi must traverse a scary (and retarded) world to return home.
The video begins at Mario's House. Luigi has just made lunch for Mario, which turns out to be poop. Enraged, Mario tosses Luigi out of the house. Just after Luigi picks himself up and checks the mail, a shadowy figure whizzes by. Luigi is frightened and hurriedly tries to get back inside the house after an Old Man asks him where the bathroom is. Unfortunately, the door is locked, and Mario is asleep. Suddenly, the shadowy figure appears behind Luigi, prompting him to flee and jump into a warp pipe with a "DANGER" sign, causing him to get warped to a Delfino Plaza-like area, falling and crash landing onto the ground.
A local resident notices Luigi and tries to kiss him back to life, which immediately wakes him up, knocking the resident into water. As Luigi begins exploring his whereabouts, a Toad merchant tries to sell him 10 Mushrooms for 10,000 coins. Luigi declines and walks away until the Toad calls him back, noticing that he's not from around here. The Toad decides to sell Luigi a gem that he says will teleport him back home. Luigi takes the gem and uses it, but after it fails to anything, he realizes the Toad was lying and throws the gem at him. Luigi walks off and tries to greet a stranger, who immediately freaks out and runs away. A policeman then unexpectedly shows up and tries to arrest Luigi for all of his previous actions, also pointing out that the man ran away because Luigi was apparently "ugly as hell". Frightened by this, Luigi flees from the scene, knocking a bag of Doritos out of a Guy's hands and into the water, causing him to cry in sorrow. The policeman catches up to Luigi and corners him, but Luigi manages to escape by jumping in the ocean. As Luigi is celebrating, however, he is promptly eaten by a Blubba.
Eventually, Luigi wakes up inside someone's house. He runs downstairs to find the house's owner, who says he found Luigi "coming out" of the fish. Luigi then tries to go outside but is immediately attacked by a barrage of Shy Guys and Koopa Troopas, causing him to retreat back inside the house. Meanwhile, at Mario's house, Mario has completely forgotten about Luigi's existence, despite the numerous Luigi-related posters around. He then notices on TV that the policeman who tried to arrest Luigi had completely exaggerated the events of the chase, and as a result, Luigi is incorrectly labeled an insane criminal. Remembering his brother, Mario goes outside and desperately tries to find him. However, he only finds an old man wearing Luigi's cap and mistaking him for Luigi, takes him in the house due to his stupidity.
Back to Luigi, he was discovered by the policeman and arrested, being put in prison and has his cap taken away from him. Upon escaping (but not before screwing up and getting beaten by guards in several areas), he jumps on a warp pipe but misses and falls into a forest. Exploring the forest, Luigi finds thousands of creatures who look like and gets frightened by their ugliness (and also realizing how "ugly" he really is). Insulted, the Luigis proceed to approach the frightened plumber, and he proceeds to pass out. Upon waking up, Luigi finds himself back at his house (along with the poop dish) and believes everything to be a dream. However, when he and Mario answer the door, they find all of the people whom Luigi met in his adventure, INCLUDING the policeman, who proceeds to beat the living crap out of him and shove him in Mario's stove.
In the credits, a scene which plays tribute to the Doritos bag that Luigi accidentally made a man drop into the sea plays.