https://www.pcgamer.com/hearthstones-next-expansion-is-called-the-witchwood/

A trio of Hearthstone developers went into the forest to discover the secrets of The Witchwood, the new expansion for Hearthstone. They were never heard from again—but we did get a pretty cool teaser out of it. 

Set in the Worgen-cursed city of Gilneas, the Witchwood expansion will feature 135 new cards, a few of them found conveniently hanging in a tree by Hearthstone head guy Ben Brode. Azalina Soulthief will replace your hand with an exact copy of your opponent's, which should lead to some interesting strategic back-and forth; there's also Genn Greymane, a neutral minion who will reduce your starting Hero Power cost to just 1 if your deck has only even-cost cards at the beginning of the match, and Baku the Mooneater, who will upgrade your Hero Power if your deck contains only odd-cost cards.