Luigi Mario is a classic major character and the deuteragonist of the SMG4 series.
He is a green-clad Italian plumber from the Mario franchise, Mario's younger twin brother/sidekick, an innocent citizen of the Mushroom Kingdom, the lover(?) of Daisy (it's unknown if they are still dating), and a loyal member of SMG4's Gang, thus so far as of 2020, the two remaining classic members of the gang, alongside with Bowser. He went on many adventures throughout the years and would often be there to handle Mario's shenanigans.
Rather than being a lovable coward sidekick to Mario, this Luigi is often portrayed as a paranoid and easily scared manchild (mainly afraid of Boos), who is often humiliated by his peers. While he does have awesome and courageous moments, they are normally very rare. He was commonly treated as a joke of bully-victim in a couple of bloopers, being called gay and someone who "nobody cares about". In SM64 Bloopers: Luigi Labyrinth, he became a villain who tried to rule the kingdom with Luigi Dolls. Despite the arguably cruel way he is normally treated, he is selfless and willing to commit for his friends.
Luigi's first appearance in the Nintendo canon was in the 1983 Game and Watch game Mario Bros. and the unrelated arcade game of the same name. In both games, he was a palette swap of his brother Mario and was controlled only by the second player. The same went for his appearance in 1985's Super Mario Bros. In both Super Mario Bros. 2 and The Lost Levels (the Japanese sequel to the first game), Luigi gained the ability to jump higher than Mario, though his traction and the fact it took longer for him to build up speed and slow down made him "more annoying" to use. Super Mario Bros. 2 also made Luigi thinner and taller than Mario.
His relevance in the Mario franchise declined in the Nintendo 64 era. He was absent in several games, the most notable (and most hated) of these absences being in Super Mario 64. Funnily enough, he was planned to be in the game but was cut due to hardware limitations. Luigi's relevance was thankfully renewed in the later Nintendo 64 games, and in the Gamecube era, he starred in his very own spin-off title, Luigi's Mansion, which saw him saving Mario from being turned into a portrait by an army of ghosts. This game fleshed Luigi out as a cowardly, phasmophobic but good-hearted and loving brother to Mario.
In SM64: Meet the Luigi, there were many conflicting reports of how Luigi became awkward and cowardly. According to Toad, Luigi was playing with a doll modeled around himself, but accidentally kicked it into a toilet. When he went to retrieve it (getting stuck in the toilet seat in the process), Wario came around and sitting on the toilet seat, proceeded to unknowingly poop on Luigi, scarring the green plumber for life. According to Mario, something bad must have happened to him in his childhood and the scene cut to a flashback revealing a Klepto kidnapping Luigi.
A running gag in the series was Luigi being abused and humiliated, such as by his own brother. When not being physically attacked, Luigi was often the victim of verbal abuse, including many accusations of homosexuality. However, he also provided much comic relief due to being the butt of so many jokes.
Originally, Luigi looked like a re-texture of his brother Mario, just like many other characters in SMG4's videos. However, beginning on March 7, 2016, his appearance changed slightly to better match his current look in the main Nintendo canon, but still as a Super Mario 64 sprite.
He once had two YouTube channels, but the first one was temporarily banned due to Luigi's intro being a ripoff, and the second one was due to Mario's streaking. However, this is only in SMG4's canon, and not in real life.
Uh, Bro? Are you sure about this?
—Luigi's cowardice getting the best of him.
Luigi is kinder and more understanding than nearly all of the other characters. He is often cheery, enthusiastic, fun, and ready to lend a helping hand. Compared to other SMG4 characters, his personality is not drastically changed from his Nintendo counterpart. He also relies on common sense, unlike Mario, who usually tries to solve problems with violence.
His main weaknesses are his cowardice (though he was fully willing to rescue his brother twice despite this), in which he gets very nervous when doing something dangerous or immoral, and his easily-exploited kindness, which often results in him being treated like a doormat. This version of Luigi is more likely to get scared than the mainstream one, already freaking out upon seeing Goombas (which funnily enough, are the weakest enemies in the Mario franchise) and knocking into a stranger's house. He is also shown in The Toadassass-ination to be stupid as he is seen protecting Koopas when Mario told him to throw them at Toad. Like his mainstream counterpart, Luigi suffers from an inferiority complex, constantly overshadowed by his older brother's popularity and basically being treated as a nobody.
"Okie Dokie, Look Out!"
—Luigi, when serious.
However, when pushed too far beyond the limits of his tolerance, he has been seen to get angry. In these rare instances, he is very unrelenting and mean, such as when he teamed up with Waluigi, though he usually reverts back to his normal personality when he calmed down.
A running gag in SMG4's videos is that Luigi has a tendency to celebrate things too early, which often results in misfortune befalling him. For example, when some of SMG3's Forces attacked him, Luigi managed to hold them off. However, even though he was still in hostile territory, he began to celebrate, which resulted in Shrek sitting on him and capturing him.
Luigi has committed various crimes in the series, most of the time by accident. He also got framed of crimes by his own brother, Mario.
Murder, Assault, and making somebody cry at his ugliness: In A Lost Luigi, Luigi accidentally kicked a man into the sea, threw a ruby into a Toad after the latter lied to him, and when he said "hi" to a nearby man, he freaked out at how ugly Luigi apparently was and fled. This led the policeman in the video to try and arrest him.
Demonic Rituals: In Mario Preschool, Luigi accidentally summoned Satan the Devil (who was revealed to be a good friend of him) while teaching preschoolers about shapes. This led to him being arrested offscreen.
Illegal Operations: In the Anime Arc, Luigi reluctantly joined the Anime Cartel (a criminal organization which, following the anime ban, smuggles the now-illegal anime into the Mushroom Kingdom), to lift the Anime ban. This charge was possibly dropped.
Despite his cowardice, Luigi has many abilities that he rarely uses on the field.
Green Missile Attack: Luigi's iconic move from the Super Smash Bros. series; Luigi charges the attack and upon finishing, propelles himself like a missile at incredible speed, hitting a nearby opponent and send them crashing into another room. SMG4: Stupid Smash Bros (where Luigi was brainwashed), SMG4: The Splatfest Incident where Luigi used it to defend Tari, and Final Hours were the only instances where the Green Missile actually failed (in the former, Mario dodged the attack, and in the latter, during the SMG4 gang's fight with Goku from Dragon Ball, Goku managed to catch said attack without flinching).
Extreme Luck: As seen in SM64 Bloopers: Casino, Cards and Chaos,he says that he is cursed with winning every game in the Casino, and he certainly does. He wins literally every game and raises enough money for the Super Spaghetti Dispenser Machine. And in SMG4: My Mario Academia, his quirk is literally extreme luck, as he rolled 5 dies and they were all sixes.
Superhuman Strength: Although not as strong as his brother Mario (who even managed to lift a control panel of a train, mind you), Luigi has a great level of strength, which was best demonstrated in High School Mario, where he managed to lift Mario (who according to New Year, New Mario, weighs 14,000 pounds, which equals 7 tons), threw a milk carton at Bowser which was somehow enough to hit the Koopa King and send him flying, and even hitting him and making him crash into a truck. In SMG4: War Of The Fat Italians 2020, he transformed into his Macho self and managed to just barely lift a gigantic Beeg SMG4, though it resulted in him being crushed.
Superhuman Speed: In Mario's Jackass, Luigi outran an ENTIRE bull stampede. Since bulls usually run at 20 miles per hour, this feat is very impressive in itself.
"Death Stare": Originating from the meme of the same name, Luigi gives a person a disapproving and menacing glare as he passes by. In Smexy Soccer, a Boo was utterly horrified by the Death Stare (which is ironic given Luigi's phasmophobia, which means extreme fear of ghosts, and the Boo is a ghost).
Superhuman Agility: Due to his skinniness, Luigi is extremely agile, being able to jump much higher than Mario. More ridiculous is his ability to dodge, as shown in Wild, Wild Mario, where he managed to dodge several gunshots from Wario and Waluigi without getting tired (though he was left traumatized from the constant dodging).
Great Dancing: Luigi is an expert dancer (having shown dancing so many times in Meet the Luigi, much to Lakitu's frustration), having practiced it many times while Mario was away.
Bilingual: Due to his Italian heritage, Luigi knows both the Italian and English languages.
Negative Zone: Also inherited from the Super Smash Bros. series, Luigi initiates a strange dance which causes a green sphere to appear and anyone standing near it to feel dizzy and trip uncontrollably. In Waluigi's Time, Mario states that Luigi can slow down time with this ability.
Poltergust: The recurring gadget from the Luigi's Mansion series, Luigi uses this vacuum cleaner to suck up any ghost he sees.
Cowardice: Luigi's biggest flaw is his extreme cowardice, which he feels whenever doing something immoral or dangerous. In the SMG4 series, this cowardice is so ridiculous, Luigi freaks out whenever he sees anything that looks scary to him (including Goombas, which are one the weakest enemies ever). He only shrugs off this weakness whenever his loved ones are in danger.
Overconfidence and Recklessness: Luigi sometimes can't help but celebrate when something good happens to him, which results in misfortune befalling him.
Super Nut: It is only activated when Luigi sees something extremely arousing, where it is symbolized in Luigi's screaming and elongated nose, as demonstrated in SMG4: War Of The Fat Italians 2020.
His old SM64 design is a green recolor of Mario.
In "Super Mario 64 Bloopers: Crystal Funhouse", Luigi is called "Luigi Gaywalker", but it is likely that "Gaywalker" is referring to his role in Mario's Star Wars battle as opposed to being his actual surname. The line "No! I like being Gaywalker!" further supports this possibility.
In "Guards N' Retards: Prisoners", "SwagQuest", Luigi is seen driving a kart and making an angry face at the prisoners (to Mario in SwagQuest). This is a reference to his "Death Stare" from Mario Kart 8, which is very popular on the Internet. The Music playing while Luigi doing it is "Ridin'" from Chamillionaire.