When the popular card game "Hearthstone" got its recent improvement, hardcore fans of the game noticed a new button on their screens. This new interface doesn't seem to have any particular use in the game, and players were mystified as to what it might signify in the weeks ahead. 

Now, developer and publisher Blizzard has confirmed that the new button has something to do with a new player versus player mode called "Tavern Brawl." The button interface will be located below the Play, Solo Adventures, and the Arena buttons on the main "Hearthstone" screen.

In addition to the mode readily available on the home screen, the new "Tavern Brawl" mode will have a unique feature — it will not have a rigid set of rules, and the rules could change every week.

According to Blizzard's announcement on its forum, "Each week, a different Tavern Brawl will pit you head to head versus another player using exciting and unique rules. One week might feature preset decks, while another week could have you crafting a brand new Tavern Brawl deck following specific guidelines, while others might offer buffs to specific minion types — who knows!" 

However, there is a minor requirement for players who would enter the event — the "Tavern Brawl" can only be accessed by gamers who have at least one character who is at level 20 or higher. 

Since "Tavern Brawl" is expected to roll out together with a new patch update, fans can expect the new mode to be made available this month, with the first event occurring in the middle of June. Blizzard has also added that as part of the celebration, the new mode will have free admission for players. In addition, gamers who win their first games in the first launch week will earn a free card pack.