Fans will remember that one goal in every level of the slightly less insane normal game was to collect eight red coins. You'll also remember that many levels had hidden 1-Up mushrooms. What you probably don't recall is that these mushrooms were designed to home in on Mario. Most gamers would grab them too quickly to notice, but if you missed one, the mushroom would follow you to prevent it from accidentally falling into a pit of lava or getting gobbled up by a stoner Koopa.
Two brilliant gamers whose names have been lost to history (in the sense that in my life's history I never learned Japanese) considered these two facts and then combined them in a way that no rational mind ever should. Their goal was to summon a mushroom and then collect all eight red coins while avoiding its never-ending pursuit.
It works brilliantly because Mario is slightly faster than the "green demon," but the mushroom displays the relentless determination of a fungal Terminator and has the tendency to give a big ol' "fuck you" to the laws of physics by flying through walls. It essentially turns the cheery and whimsical Super Mario 64 into a survival horror game. You never know when the mushroom will pop up, but you do know that it's always out there. Watching you. Hunting you.