Update, 5/4/18: Blizzard has announced that Hearthstone's next expansion, The Witchwood, will release on Thursday, April 12th.
Once players log into Hearthstone after The Witchwood's arrival, they'll be able to download three card packs and a random Class legendary card - all from the new expansion - for free.
Blizzard also notes that it will be bringing its Witchwood card reveal season to close in a livestream on the official Hearthstone Twitch channel on April 9th at 6pm GMT / 11am PDT.
Original story, 13/3/18: Wolf-beasts and witches star in Hearthstone's next expansion The Witchwood, due to launch in April.
Remember the Warcraft zone of Gilneas? Its spooky forests and worgen inhabitants are the setting for Hearthstone's next batch of 135 cards.
Single-player content is coming, too - a new mode named Monster Hunts, although details are scarce.
The Witchwood's more granular additions include two new keywords - Echo and Rush - and beastly minions with big buffs if you use only odd or even mana cards.
Cards marked with Echo let you play them multiple times in a turn - as long as you have the mana to do so.
Rush, meanwhile, acts like Charge - except minions labelled with it can attack only minions (and not heroes) on entering the battlefield.
Here's Hearthstone's Ben Brode and co. stomping round a forest finding new cards from the set:
Blizzard's usual offer of 50 packs and an exclusive card back is now available to pre-purchase through the game, priced Ł44.99.
There's no firm release date for The Witchwood yet, except for that April window. Expect more on Monster Hunts - the single-player mode - soon, though it won't launch until a fortnight after the expansion goes live.