As told by Nerdy in First episode, the only rule of the Mario Fan Club is that all the members must love Mario, hate Bowser and even hate Bowser Jr (presumably for disintegrating his face earlier in the episode.)
The members unite in a tall, red building that says "Mario Fan Club" on it with big letters. It is located next to an unknown street and some trees. They may also have a reunion outside of the building, like in Living with Nerdy. When united, they wear Mario's typical videogame outfit (a red hat and long-sleeved shirt, blue overalls and brown shoes.
Inside the Mario Fan Club main bulding there are many arcade games based on Mario, which the members play when idle. However, there are some organized events held inside, like the game "Throw stuff on the Bowser Jr statue", where the members throw various objects at a big, grey, Bowser Jr statue, while booing at Bowser Jr. Other events outside the building include scheming attacks against the Koopa family and so forth.
Inside the tall, red Mario Fan Club building there are various arcade games based on Mario. There are also toys based on Mario, and posters of Mario attached to the big, blue wall, for example, a Mario Strikers Charged poster with Mario on it. There is also a big Mario statue made of gold inside the building, but its purpose is unknown.
The Mario Fan Club was shown in it's headquarters in First episode Part 3 when Bowser Jr fell through the roof. They thought that he was a new member and Nerdy introduced him and explained the rules of the club. When they realized that it was Bowser Jr. In disguise they collectively blew garlic breath at him and then Bowser Jr turned around and defected the garlic breath, causing Nerdy to lose his skull.
Living with Nerdy Part 2
The Mario Fan Club had their most important role in Living with Nerdy Part 2. While Nerdy is temporarily living in the Airship, he makes a secret plan with the Mario Fan Club where he secretly has the club manufacture a statue of Bowser and trick Bowser into accepting the statue as a gift. Josh and other Mario Fan Club members secretly hids in the statue and came out and attacked the airship. They tried to take over but were defeated.
Two Koopas for a throne Part 1
At the ending of part 1 Josh told Nerdy that they are making a new plan against Bowser Jr but they are going to wait until Nerdy recovers.
To be continued
- There is a golden Mario statue in the building, and, ironically, in the 3DS game New Super Mario Bros 2, there is a power-up that turns Mario gold, much like the statue. The episode where the statue is first seen was released in the March 2011, while the game was released in mid-2012.
- The closest in real life to the fictional Mario Fan Club is Nintendo's Super Mario Club at http://www.supermarioclub.com, although they're not evil.