There have been many variations of Mario. This was fully shown in The Grand Mario Hotel.
The Mario of the SMG4 Universe is the central character and one of the two main protagonists of the SMG4 series. He is very dumb and can also be violent, often leading himself and his friends into trouble. He also loves spaghetti, despite the fact he doesn't know how to make it himself. He's shown to not like his brother, Luigi, and is very lazy.
Dr. Mario is the doctor version of Mario and is about the same in terms of intelligence and competence. He sucks at being a doctor mainly by being distracted several times. He is the main character in R64: A Dose of Dr. Mario and R64: An Overdose of Dr. Mario. He's shown to be a separate person from Mario as shown in SM64: ṩṩἔᾗмὄḋᾗᾄʀ 9 - Time travel edition and SM64: Super Mario RUN RUN RUN!.
Paper Mario is the paper variant of Mario who lives inside a book containing the Paper Mario universe. He usually appears in SMG4's earlier videos in the Paper Mario scenes and sometimes in the rare clips of Paper Mario Thousand Year Door. Paper Mario is rarely seen in any of the newer videos (save for a few cameos in the videos and thumbnails for them). Paper Mario even got the major role in the 2017 video SMG4: Stupid Paper Mario.
Bootleg Mario (Also known as Grand Dad) is a bootleg version of Mario. He first appeared in SM64: THE BOOTLEG DIMENSION where he was freed from the Bootleg Dimension by Mario. He has the ability to turn characters and landscapes into bootleg versions through touch or by zapping them with a laser. He appeared in SMG4: Welcome To The Kushroom Mingdom as the "Ghost of Sh!tty Games" where he grants SMG3's wish to build a kingdom similar to the one he lives in except more "cooler".
Mario Head (also known as Mario's Ugly Head or The Giant Floating Mario Head) is the head version of Mario from Mario Teaches Typing 2.
He's similar to regular Mario, as he likes spaghetti just as much as him. But he is shown to be a lot smarter than him.
In The Grand Mario Hotel, it's revealed that he hates it when people use bad grammar.
Hobo Mario (Also known as Ugly Mario) is an ugly and distorted clone of Mario. He first appeared in SM64 Bloopers: Casino, Cards and Chaos.
Baby Mario is the baby version of Mario. He is sometimes depicted as a sprite or, at other times, a 3D model. He made his first appearance in Super Mario 64 Bloopers: The Babysitters.
Sometimes Mario will scream "I won’t live to see my Baby Mario".
Don Mario is the one who runs the Grand Mario Hotel. He's Dumbledore from the Harry Potter franchise with Mario's mustache and cap.
In The Grand Mario Hotel, Don Mario decided to invite SMG4's Mario to the hotel, which leads to him getting injured and unable to run his hotel. He tries to get Mario to tell Smart Mario to run the hotel, but Mario assumes he wants him to run the hotel. After all the other Marios retaliate on him, he and Smart Mario resurrect Don Mario using a 1-Up Mushroom.
Kawaii Mario is an anime-like variation of Mario. He wears a dress, pink ribbons, and has rosy cheeks.
Mario's Brain lives inside of Mario and is one of the main sources of Mario's body, controlling most of him. Luigi bribes it to attack the Virus.
Mario Maker Mario
Mario in his outfit from Super Mario Maker.
He appeared as an actual character in The Grand Mario Hotel.
Mango is the main antagonist in SMG4: The Tari Abnormality.
Mango was a character from the Super Smash each other in the ass Bros. series. According to Mango himself, he doesn't like fighting, yet has been doing so non-stop for 56 years straight. Worse, the developers keep nerfing him with every game. Thus, Mango considers his life an "infinite hell". He was shot and killed by Mario "for posting cringe".
Shadow Mario is a doppelgänger of Mario. He appears in Mario's EXTRAS: The Grand Mario Hotel, where he writes Mario Sucks on purpose to get the Mario’s in a fight.
Soccer Mario is the Super Mario Strikers version of Mario.
He ask Mario if the Hotel has any classes. Mario directs him to the syndicated drowning class. Soccer Mario happily joins.
Smart Mario is a taller, more realistic version of Mario with glasses and a graduation hat, and as the name suggests, he is a lot smarter than stupid Mario.
He only appeared in The Grand Mario Hotel so far, where he was the first Mario variation to meet SMG4's Mario.