World of Warcraft recently released its latest raid, The Nighthold, and Blizzard has implemented a nifty Hearthstone easter egg for those that complete it.
Gul'Dan stands as the final boss before player completion of the raid and it turns out he has a chance to drop a new toy for Warcraft players, Golden Hearthstone Card: Lord Jaraxxus.
Somehow, despite all the fighting it's still in pristine condition according to the description so you may want to be a little more careful than Gul'Dan was. And what does it do? Exactly what you'd expect! "Use: Destroy your hero and replace it with Lord Jaraxxus," but unlike Lord Jaraxxus this one has a 2 hour, 30-minute cooldown.
It looks like Blizzard sneaked this one into the final release as it is not listed on the raid's loot table. During beta, players could get a "Pack of Hearthstone Cards" instead which contained Eye for an Eye, Wisp, Blood Imp, Young Dragonhawk, and Angry Chicken. Needless to say, this has been quite an upgrade.
If you're actually interested in completing the raid for yourself and having a chance at getting this drop, Wowhead has written up a raid survival guide.