The 2012 ChinaJoy Cosplay extravaganza was especially extravagant in this case, as an entire stage is decked out with League of Legends cosplayers.
It's not just the quantity that's impressive, it's the quality of said quantity. Also of note? The prolonged pose-holding. These cosplayers are serious.
A few weeks back I made a concerted effort to get into this game. It's going... OK. I'm not quite at the stage where I travel to China in costume though.
Unbelievable League of Legends Cosplay Show [Fashionably Geek]