Blizzard just shared an important reminder for players who have Hearthstone installed through the Amazon Appstore. While it’s not a very common Appstore, some players might still use back from the time when purchases through Amazon Coins were popular. But right now Amazon Appstore is closing down soon, and if your account isn’t connected to Battle.net, you might lose your in-game progress.
You can play Hearthstone on a “guest account”, without connecting to Battle.net account. It’s automatically created when you launch the game if you choose to not log in. You can’t make any in-app purchases, but you can progress (play matches, earn packs in game, craft cards, and so on). While I don’t know how many players play that way, the number is definitely higher than 0 if they’re sending out this announcement.
If that’s you, in order to save your progress, you simply need to connect your guest account to the Battle.net. Then once the Amazon Appstore closes down (or earlier), you can just download the game from another source and use that Battle.net account to login.
You can learn more about how to do it on this support page.
