It is illegal to download a ROM of Super Mario 64 unless you physically own the original cartridge and dump it yourself.
The Z64 USA version of Super Mario 64 has been a favorite among speedrunners due to its relatively stable and well-understood nature. Many world records have been set using this version, with players continuously pushing the limits of what's possible in the game. The game's physics, glitches, and mechanics have been extensively studied, allowing speedrunners to execute incredible maneuvers and shave precious seconds off their completion times. super mario 64 rom z64 usa