Pre-Classical Era (Mario/Servbot to Jill//Link): This was the early days of the contests when they were a GameFAQS only thing, and we had no idea what would happen or what to expect from them.
Classical Era (Sonic/Samus to Final Fantasy VII/Suikoden II): The contests were not just a GameFAQS thing, and votals expanded. We knew what to expect more, but we were not dominated by stats and patterns. This was the prime time for GameFAQS contests, in my opinion.
The Dark Ages (Pokemon G/S/C/Xenogears to Link vs. Sephiroth): The poll was moved down and votals dropped, interest died off at times during this period only to be revived during 2005.
Modern Era (Legend of Zelda/Civilization to 2007 Contest (no real specific match)): Votals exploded and people were really interested in the contests during this time. Lots of stuff was happening in the gaming world and there was the potential for changes in the contests.
Postmodern Era (2007 Contest to Sora and Riku/BJ and Hitler): The very concept of contests was subverted in this period with stuff like 4 ways and joke characters/4chan rallies, 12 hour matches, etc. etc. While we worked on perfecting certain aspects of contest analysis during this period, we also came to understand much more about how variable results can really be. I don't really have a starting point for this era. Either the first match of 2007, Mudkip/Bidoof's R2, or L-Block's R2/R3 would be good picks I guess.
Neoclassical Era (Mario and Bowser/Ike and the Black Knight): BJ and Hitler failed to bring in joke rallies, and a lot of conventional parts of contests seem to have returned, albeit in a much more boring manner.
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My bracket wasn't good enough to beat SuperNiceDog's in the GameFAQS Rivalry Rumble. Congrats!
This is Yesmar.