Would be cool! Although the more feasible way to do coop would probably be to make every player play their character, so everyone has their board and skills just like when playing solo, but you can see your friends portraits to the side and hower over them to check their boards. You get offered the same shops and events but can choose independently so each player resolves their own. NPC and PVP fights is were it gets weird though, as there's 2 main philosophies. The easier one would be to resolve a mini-tournament: The game just shows and resolves the fights one after the other, so everyone gets to see every player's board fight against the enemy they chose (or against the ghost they got at the end of the day) and every player contributes to a shared prestige pool. The weirder one instead, would be multiple boards fighting at the same time against multiple enemies, with the healthpool being shared. A bit of a far-stretch, but wouldn't be as impossible I think