Argul's Tomb is content that will be available 30 or so days after today's (8/14/12) launch of Darksiders II.
Once the content is released and becomes available for download, your codes should work. If at that time they do not, please submit a ticket with THQ Customer Support - support.thq.com/home
Follow these below steps to redeem your Argul's Tomb Pass:
1.) If you are not logged into to Darksiders.com you should do so in the upper right hand corner of the site by clicking 'login' or 'register' (This step is not required)
2.) Head to Whoops! Browser Settings Incompatible
3.) If your logged in your e-mail will be filled in for you, if you are not logged in, input your current e-mail address and select your region and platform of choice
4.) Now input your token that is printed on your insert or that was provided via e-mail
5.) Click Submit
6.) If you input your code properly you will see a 'Success' screen and you will get an e-mial at a later date letting you know when the Argul's Tomb content becomes available.
Need to see these steps in person? Check out the following video.
Darksiders II: Argul's Tomb Redeem Code Process -