The game was ahead of its time: it not only included a bog-standard Story Mode where pre-defined characters delivered one-liners to each other and the ending resolved their conflicts, but a Tournament Mode where you create a character and follow them up the tournament ladder, buying different robots and training your skills and enduring one-liners from the bad guys. This way of grafting RPG / sports elements onto a fighting game (usually known for their extreme shallowness), plus good market positioning as a PC title, inspired a hardcore fan following that lasted for about 10 years.
So this guy, unknown to me (as they usually are), has taken every single one-line taunt in the game and written his own cocky one-line response. It's like he's created his own story mode character and written the 'missing' half of the dialogue for it. This isn't fan fiction in the traditional sense of appropriating the story for your own ends, it's writing yourself into the existing storyline through a different medium. (And, of course, fanfic is 90% female and this guy's taunts are heavy on the testosterone.)
I'm sure he's not alone - he can't be the first person to take a silent protagonist and write a script for them, for non-subversive purposes. Game studies too often focuses on the feminist end of fan creations, the kind that Breaks The Rules. Having a legitimate Mary Sue character is very interesting and it seems to me hitherto unexplored.