Okay everyone saying they are a beta tester, or that they work at blizzard and know the code are morons..

Everyone that attends Blizzcon get's a little bag of stuff in it, and one of the things is a code, you input that code here: [url]http://www.worldofwarcraft.com/misc/pet-redemption.html
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Then the site will give you ANOTHER code that you use in-game to get the murloc pet/costume!

Also: there isn't 'one' code, it works like CD-keys, you get your code and once you use it, it is disabled.