The biggest rivalry I saw from my limited vantage point watching all the early IGAU tournaments on stream and knowing some of the people who go to EVO, it seemed like NRS vs. FGC was the biggest one. Like, the NRS scene come into being with MK9, but didn't get much respect from the rest of the FGC, the SF people in particular. When IGAU came out, there was a wave of folks from other games coming in, many with the attitude of, "you NRS guys suck, you are all free, I'm going to show you what a real strong player who plays in real competition is like, I'm going to body you, MK is a crappy game that just relies on blood to sell," and such.
Of course, not everyone was like this. I am definitely not saying that everyone was like that, and there had been players in MK9 that played in other scenes too (like Justin Wong). Chris G had been around in MK9 and seems like a pretty quiet guy. Balrog got into IGAU and I don't recall hearing anything other than that he was a nice dude. Yet there were others, probably the most notable being KDZ since he was the first big dog and was saying things like, "there's no one else in this game even in my league," and also Filipino Champ popping off. Some were saying Champ was just doing it to build up hype, I don't know him. Another that sticks out is that guy who played Ares in an early tournament and was being really insulting to Tom Brady and other players. I forget his name or what game he was from, but he had come up with a different way of playing Ares that no one was used to, so he got pretty far in that tournament.
In the end, I think the NRS scene held its own and earned some (hard fought) respect from other scenes. I mean, if people from other games just jumped over into IGAU and started wiping the floor with everyone, filling every top 8, that would've sucked. That TYM regulars, like Pig, held the fort was cool.
If there's an IGAU2 rivalry to look out for that is the meta-rivalry that explains many rivalries. We'll see if it repeats and we get Round 2 of NRS vs. FGC. It wouldn't surprise me if we see some players from SF, KI, and such coming into IGAU2 to try to grab that prize money.
