There's a good chance that a future update for Hearthstone will add co-op gameplay into the competitive online multiplayer card game.
Players have been speculating for a long time that Blizzard has plans to add a cooperative mode into the game that allows players to team up against the AI. This speculation has resurfaced with newly discovered code in the game's latest update.
When Blizzard released the 3.0 update this past Tuesday, which adds support for the upcoming expansion, The Grand Tournament, a reddit user named Insydr datamined the files and discovered references to co-op mode, including audio and text.
Here's what it says:
Added VO_HRW_TEST_00.AUDIOFILE: "test"
Added VO_HRW_TEST_01: "Well done! You've defeated the boss together.\n\nBoth players win!"
Added VO_HRW_TEST_01.AUDIOFILE: "test"
Added VO_HRW_TEST_02: "Defeat Gearmaster Mechazod together to win!"
The code clearly implies that players will be able to cooperate to defeat bosses together, perhaps in a future expansion pack that's yet to be announced.