Since 2011, they've been up to hilarious, scary, random, and epic misadventures and shenanigans. However, come 2018-2019, 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 incredibly dumb. 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 been mostly seen being absent during The Anime Arc, but reappeared in late 2019.
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. 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 primary antagonist of The Rapper Bob Arc.
Meggy Spletzer - Formerly a female Inkling transformed into a human who was accidentally captured in a paint bucket, causing her to be freed and flee into a manhole that leads to Inkopolis, taking Mario along with her. She completes in Turf War tournaments with her team, the Splat Squad. After the events of SMG4 Movie: Meggy's Destiny, she fulfilled her dream becoming a Splatfest champion, and later moved to the Mushroom Kingdom and intends to have a career of crime-fighting.
Shroomy - A young anthropomorphic mushroom and a member of the Mushroom Scouts with over 300,000 badges to his name.
Saiko Bichitaru - A 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, the Inkweaver.
Toad - A cynical and annoying mushroom person which that his behavior is probably due to Mario's antics and probably left the gang in favor of Shroomy. Like Bowser, He is mostly seen being absent around the gang during The Anime Arc, and recent episodes, but still appeared among the gang in SMG4 Movie: Meggy's Destiny. Due to his infrequent appearances during Season 9 and Season 10, it's currently unknown if he is still a member of the gang or retired.
Peach Toadstool - 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 oftentimes allied with the gang. She is also one of the two main antagonists of Part 1 of The Anime Arc, alongside Desti.
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 insulting Minecraft in any way will result in getting on his bad side. He served a lot of purpose in earlier bloopers but stopped appearing with the gang as of Season 8. After that, he mostly appears in Minecraft-themed bloopers such as SMG4: If Mario Was in... Minecraft and SMG4: The Minecraft Plague.
Starman3 - A former friend of SMG4. Due to real-life controversies, he has been removed from SMG4's videos.
Xboxfan997/X - He used to be in 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.
Chris Gordman - One of the main protagonists of Guards N' Retards along with his partner Swagmaster69696969696 who used to 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 tertiary antagonists in the The Anime Arc previously.
JubJub Boopkins - Fishy Boopkins’ younger brother who is often bullied by Mario.
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.
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. He played a major role in SMG4 Movie: Meggy's Destiny.
Yoshi - A green dinosaur who is acts as an ally of the Mario Bros. He is usually depicted as a fruit lover, wallet thief, drug user, weapons dealer, or even a tax fraud criminal in the series. His personality seems to wildly vary with every episode he shows up in.
Jeeves - A sentient fork who owns several companies.
Joe Boopkins - Fishy Boopkins's father. He's basically a giant version of Octodad with Cthulhu's head.
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. He is currently seen being the only enemies who actively antagonizes the gang.
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 the game Super Paper Mario and the primary antagonist of Part 2 of The Anime Arc, as well as the main antagonist of arc overall. He is the boss of the Anime Cartel and requires the assistance of SMG4, Bob, and Fishy Boopkins to escort Saiko to Japan, He forms a temporary alliance with Mario, Axol and co. to get anime un-banned 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. He later celebrated with Christmas with Mario and co. after receiving a gift.