Since 2011, they've been up to hilarious, scary, random, and epic misadventures and shenanigans. However, come 2018 to 2019, they've been involved in dramatic and rather emotional and serious adventures in story arcs such as The Waluigi Arc, The Rapper Bob Arc and The Anime Arc.
SMG4 - The creator of the bloopers and one of the two protagonists of the series. He resides in Peach's Castle with Mario, often making his bloopers (or playing Minecraft), and gets generally annoyed by Mario (who is apparently his assistant), but he likes him nonetheless.
Mario - The other protagonist and central character of the series. He is crazy for spaghetti and extremely retarded. Almost all of the bloopers revolve around him and the trouble that he gets the main cast and himself into.
Luigi - Mario's younger brother and the deuteragonist of the series. He makes smarter decisions than Mario, but he's still as cowardly as he is in the actual games, if not more so.
Bowser - The so-called big bad of the Mushroom Kingdom who's always trying to kidnap Princess Peach. Despite this, he is actually one of Mario's friends. He isn't very smart as his Super Mario counterpart and commonly falls victim to his own incompetence. He temporarily left the gang during The Anime Arc, but rejoined in late 2019.
Fishy Boopkins - A Spike who is a huge otaku fan and has a love for dakimakura pillows, First appeared in the "Seaside Stupidity" two-parter. After his debut, he made a few more appearances before finally graduating to major character status.
Bob - A Garo who evidently was a sewer wizard from The Legend of Zelda: Majora's Mask. Mario and Luigi first me him in SM64 Bloopers: Can Ganondorf come out to play?. He's obsessed with fame, money and getting the most screen-time in his appearances. He speaks in the "WillFromAfar" text to speech voice from Acapella. Despite his humorous punching bag status, Bob has proven he can be a downright repulsive, self-admitted bastard if he isn't given the attention he wants, especially since he is the main antagonist of The Rapper Bob Arc.
Meggy Spletzer - Formerly a female Inkling turned human that was captured in a paint bucket, causing her to run amok and flee into a manhole that leads to Inkopolis, taking Mario along with her. She completes in Turf War tournaments with her team, the SplatSquad. She was very popular in her debut episode and quickly became a fan favorite. After her reappearance in The Mario Channel: MARIO'S CHALLENGE, she was promoted to major character status and has made regular appearances since then. After The Anime Arc, she was transformed into a human.
Shroomy - A young anthropomorphic mushroom and a member of the Mushroom Scouts with over 300,000 badges to his name.
Saiko Bichitaru - An beautiful but insane love interest from an unnamed dating game based on Doki Doki Literature Club. Boopkins brought her to life one day with Kamek's wand, but their relationship ends in tragedy. However, she has since recovered from said incident and has considered Boopkins a friend, though she remain a psychopath.
Tari - A shy blue-haired gamer who tends to get hurt a lot. Mario turns to her for guidance on how to be a good player and kick SMG4's butt at Super Smash Each Other In The Ass Bros, and as such became friends with them both and the rest of the gang, namely Meggy and Saiko.
Axol - An Inkopolis-born anime artist from Japan who can create anime characters using his special pen, Inkweaver.
Starman3 - A former friend of SMG4. Due to real-life controversies, he has been removed from SMG4's videos.
Princess Peach - The ruler of the Mushroom Kingdom and the castle Mario and almost everyone else resides in. She was the prominent female character in early bloopers until Meggy took over that role in late 2017, hence explaining her recent lack of appearances. However, she is still often times allied with the gang. She is also one of the two main antagonists of Part 1 of The Anime Arc, alongside Desti.
Toad - A cynical mushroom which is probably due to Mario's antics and probably in favour for Shroomy. His appearances are limited since Season 9.
Xboxfan997/X - He used to feature a lot in SMG4's videos but within 2015, his appearances have been mostly restricted to just being the host of the War of the Fat Italians series.
FightingMario54321 - Another friend of SMG4. Like Nintendofan997, FightingMario54321 has fewer appearances starting from 2015, being relegated to just cameos.
Steve - The default avatar used in the world of Minecraft but a character in the SMG4 universe. He's usually friendly with the rest of the members although calling anything related to Minecraft bad names will result in getting on his bad side.
Jeeves - A sentient fork who owns several companies.
Greg The Alien - An alien from outer space. He was captured and sent to Area 51 but was bust out of the area with Mario's help. He was grateful for it and has since stayed as Mario's House's new resident.
Chris Gordman - One of the main protagonists of Guards N' Retards along with his partner Swagmaster69696969696 who used work as guards at Fresh Spaghetti Tubbie. He's much more competent and sane than Swag is. Despite Chris and Swagmaster allied with the SMG4 crew briefly after. He and Swagmaster69696969696 have been playing antagonistic roles in the main SMG4 series previously.
Professor E. Gadd - One of the main characters of Luigi's Mansion and its sequel. He started off as a bit character in early videos but has become a recurring character as of 2014.
Yoshi - A green dinosaur who often resides on the roof of the castle. He can be a nice guy... or a wallet thief/drug dealer unless he's the one being drugged, that is. His personality seems to wildly vary with every episode he shows up in.
Toadsworth - An old Toad who tries to keep Princess Peach from being kidnapped.
Old Man Hobo - A recurring side character based on the sprite of the infamous Old Man from Pokemon FireRed and LeafGreen while laying down.
Joe Boopkins - Fishy Boopkins's father. He's basically a giant version of Octodad with Cthulhu's head.
Sonic - The main character of his namesake series. He briefly helped Bowser stopped Princess Peach from being engaged by Dr. Eggman in Egg and Peach.
SMG4's Minion - A clone who is created after Mario accidentally clones SMG4 and spaghetti at the same time.
New Super Duper Mario Plus Ultra - A descendant of Mario 500 years in a Bad Future where Weegee Dolls reign. He teams up with Luigi, Boopkins, and Shroomy, who were frozen for 500 years, to undo the Weegee Uprising.
SMG3 - SMG4's arch-nemesis and evil clone and possibly the main antagonist of the series. He mainly wants to kill SMG4 and his friends and take over the world, though on some occasions he isn't as harmful as he seems.
Wario - Mario's greedy arch-rival who starred in "The Wacky Wario Bros." episodes for a while alongside Waluigi. He loves money.
Waluigi - Wario's partner/brother. Also the arch-rival of Luigi who starred in "The Wacky Wario Bros." episodes alongside Wario. After harnessing the power of rejection, he became the main antagonist of The Waluigi Arc
Francis - An anime-obsessed chameleon originating from Super Paper Mario and the main antagonist of Part 2 of The Anime Arc. He is the boss of the Anime Cartel and requires the assistance of SMG4, Bob, and Fishy Boopkins to escort Saiko to Japan, however he makes Mario stay behind and make up all his lost money. He forms a temporary alliance with Mario, Axol and co. to get anime unbanned in the Mushroom Kingdom. He's also the mastermind behind the mass kidnapping of Inklings and Octolings, and plans to use their ink to power the Ink Weaver to 100% so that he can have an island of anime waifus. However, due to Mario and friends and the A.S.S.'s meddling, Francis is defeated and supposedly killed.
A.S.S.: Princess Peach's anime prevention force. They are the Anime Cartel's enemies. Despite being officially disbanded in SMG4: Mario Saves Anime, they help SMG4's Gang fight Francis and the Anime Cartel.
Roprinplup14 - Also known as Enzo. He was originally one of SMG4's friends. However, after Mario ruined his birthday party, he turned evil and went on a killing spree with the intent to murder Mario and his friends.
By Season 10, only Mario, SMG4, Luigi and Bowser would remain as the initial members of the gang from Season 1. Toad and Princess Peach, on the other hand, left completely starting from Season 9 due to Toad rarely ever wanting to hang out around Mario and the rest of the gang and Princess Peach due to prominence roles of the new female characters.
Swagmaster and Chris became more prominent recurring characters outside their own series since it eventually merged with the main SMG4 series in 2019 and allied with the gang.