Super Mario Challenge

The Super Mario Challenge is the shared name of a supposed challenge that can reward several things. Below are some of the several incarnations of the Super Mario Challenge:

Chain-Mail
There is an image that has appeared on Super Mario 64-related Discord servers that has an image of Mario and text that says "TAKE THE SUPER MARIO CHALLENGE" and "COPY AND PASTE THIS IMAGE INTO EVERY SERVER YOURE IN". There is no outlined reward for "taking this challenge". There are other versions, though these are likely unrelated, such as "TAKE THE SUPER MARIO CHALLENGE, CHOKE ON A BAR OF SOAP". It is currently unknown if it is tied to the other forms of the Super Mario Challenge, though due to being a Mario-related challenge and sharing it's name, it will be grouped with them.

Magazine
There are reports of a supposed magazine that details a Super Mario Challenge to unlock Luigi in Super Mario 64. The reports of the instructions vary, but below is the most common interpretation:

" THE SUPER MARIO CHALLENGE

Ah yes, Super Mario 64, what a classic. But, there's something you're missing: The Super Mario Challenge. There's a challenge to find Mario's brother, Luigi. Didn't you notice he was missing? Bowser's at it again!

First, you need to get 120 stars. This isn't an easy task, but Bowser locked Luigi up tight!

Second, you need to get to the cannon in the Castle Grounds and shoot into the stained glass on the castle. There will be a hidden slide that will have a 121st star.

Once it's complete, you need to get back up the endless stairs. It'll be very long again. You'll need to use a tactic known as a Backwards Long Jump to get back up. Consult page 23 on how to Backwards Long Jump.

Once you get back up, don't go back to Bowser in The Sky. You need to jump into the Bowser painting. There will be a new level called Bowser in the Eternal Fort.

You must beat the level, and meet Bowser once again. He'll use your own tricks and equip the Metal Cap. You'll need to trick him into running into his bombs. When you defeat him, he'll drop the key you need.

Then, get to the roof of the castle. Get the Wing Cap and fly into the waterfall. The wall behind it should break, and you'll be presented with a key door. Unlock it, and you'll end up in a level called Mario's House. you need to ground pound part of the floor in this level, and you'll find a 122nd star. When collected, you should be presented with a cutscene of Luigi getting out of bed, walking out of the house, which will appear in the Castle Grounds, and open a letter. Mario will be taken by Bowser this time. Have fun with new game+! We'll let you learn about Luigi's special abilities yourselves!"

It is currently unknown if this was a joke magazine, a magazine detailing how to unlock Luigi in a personalized copy, or a made-up magazine altogether.

Super Mario 64 DS Minigame
In some reports of the Super Mario Challenge, it appears as a minigame. It can be found by catching the Purple Rabbit, a 9th Glowing Rabbit, every other minigame, and Waluigi. Most people say that it is a hard mode of Super Mario 64, that when beat can unlock Waluigi, nothing, or something else.