N'zoth, the Hearthstone expansion's second old god, is built around the "deathrattle" mechanic.
Blizzard has been slowly revealing Hearthstone cards for its upcoming Whispers of The Old Gods expansion, and now it's revealed one of the expansion's major players: the second Old God. N'Zoth, The Corrupter's appearance in Hearthstone actually marks the very first time he is depicted in Warcraft lore. While his influence has been seen on many of the major calamities that have afflicted the world (of Warcraft), he has never actually been shown before.
Check him out in all his golden glory:
As you can see, his "gimmick" if you will, is built around the deathrattle mechanic. With both Goblins vs. Gnomes and Naxxaramas leaving the standard format, his effect isn't quite as powerful, although when paired with classic minions like Tirion Fordring and Sylvanas, he can really turn games.
Additionally, Blizzard has revealed a bunch of new cards since we last checked in, including some new deathrattle cards that should have good synergy with N'Zoth: