Hearthstone’s set rotation is happening next week! The current Year of the Gryphon will be replaced by the Year of the Hydra come 12 April 2022, which is also when the Voyage to the Sunken City expansion goes live.
Naturally, the Year of the Hydra marks the rotation of several sets from the Standard format. These include Ashes of Outland, Scholomance Academy, and Madness at the Darkmoon Faire. The Core Set also sees an update; 57 cards are taken out, and they will be replaced by 72 cards.

The 72 cards that will be a part of the new Core Set are not new cards. Rather, they are cards released in previous expansions, and some classics that are returning include Reno Jackson, Brann Bronzebeard, Elise Starseeker, and Sir Finley Mrrgglton. Yes, the original League of Explorers are coming back to the Standard format.
The Year of the Hydra rotation in Hearthstone will happen on 12 April next week. The Voyage to the Sunken City expansion will also go live on the same day. More details on the expansion and set rotation can be found here.