Simple enough- the Duels format is my personal favorite, but unlike Battlegrounds, there’s no way to play it with a friend. Obviously, there’s risk of rating score cheating, but it doesn’t need to affect that and I don’t necessarily want to fight anyone else, just play around with deck building and treasures with someone I know. All of the fights would be against the other, or perhaps by looking to multiplayer Battlegrounds, allow you to form a party with an AI competitor if left with an odd amount of players.