I spent quite some time thinking about how one could design a “classic” PnC multiplayer AG.
The main problem with multiplayer games is that you have to coordinate the presence of said players. In a MMORPG, if a teammate isn’t there, his own fault - he’s going to lose all the exp and stuff in the quest. In a competitive game, who cares - I’m going to challenge another player.
But in adventure games, if we want to be as classic as it can be, either you block the player’s advancement as long as someone isn’t playing, or you allow players to lose part of the story if the teammates solve stuff while he’s not there.
You could make parallel lines, where the interaction between different characters is restricted to some puzzles which can be solved anyway by a single player so they don’t get stuck if someone stops playing… who knows.
Or you could make it competitive