All you have to do is observe five occurences in a row throughout the weekend, and you win! What, you ask, do you win? The satisfaction of a full and fulfilling BlizzCon weekend. I don't know about you, but if I leave Anaheim having seen a new Diablo, new midlevel content, or just a really quality Murloc costume, my weekend will be made.
And while lots of these are easy to recreate yourself (anyone can complain about their class), remember: no cheating! You must observe what happens, not cause it in any way. Good luck!