Cultists, and Tentacles, and Wispers! Oh my!
The rotating card carousal on the official Hearthstone site has been updated with a different set of cards! This has happened in the past when Hearthstone wanted to tell us about upcoming content such as when Blackrock Mountain was teased.
They are themed around dark magic, cultists, and tentacled beings. Woo! The official expansion announcement comes to us on March 11th.
Thanks to IcyVeins for the tip.