Knights of the Frozen Throne already introduced a solo mission in Hearthstone that pits the player against the Lich King at Icecrown Citadel. Blizzard is now allowing the community to pair up for raid battles against the same supreme foe as part of the new Fireside Brawls.
The featured mode is currently only available on the show-floor of Gamescom 2017 and forces both players to use pre-constructed decks in every match against a Lich King that has 999,999 health. On the other hand, each player starts with 10 mana crystals and just 20 health instead of the normal 30.
The duo system works by having the second player take over immediately once the first player dies. The goal is to defeat the Lich King but it is impossible for a single pair to do so. Hence, the job falls to the attendees at Gamescom 2017 as they all keep chipping away at the monstrous health points. Hearthstone rewards the players with ranks based on the amount of damage done on an individual basis.
Blizzard plans to bring the raid battle to the rest of the public once it is done with the convention in Germany. The monthly Fireside Brawls are exclusive to Fireside Gatherings. In other words, players must attend local events to be part of the action. It will be similar to how players are joining forces at Gamescom 2017 against the Lich King. However, his health points may be reduced to make it easier for smaller groups to attain victory.