If you're looking for the article about Challenge Modes Sets, click here for the preview.
In this article, you're going to be seing videos of all the sets, because they have a rare proc animation, meaning you'll see the effect after/while casting certain spells. Every spell has its unique proc.
Other classes have not had their unique proc discovered as of yet, but I'll update it when they do.
Challenge Sets are mailed to you, once you complete certain Challenges on your realm. These have no stats and serve for transmogrification only.