Mega Man X3 is the third game in the Mega Man X series, and the last one to be released on the SNES.
This is the first actual "100%" run of this game. Hetfield90 speeds through the game very rapidly, collecting all heart tanks, subtanks, Ride Armor modules, upgrades and finally the Golden Armor. However, contrary to the previously labeled 100% run, Zero is sacrificed and his Z-Saber obtained.
The page Mega Man X Tricks explains some of the tricks that are used in this tool-assisted speedrun.
See also the any% run, which doesn't collect the upgrades but also collects the Z-Saber.