oh, it's hard... because, to make multiplayer, it took web socket to gain client-server data transfer in which, you gotta understand the difference between server and client. And thus, multiplayer in Castle meaning shared actor and stuff is kind of needed some sort of acknowledgement on sharing on the actor from client to server, and so backwards.
...
Which mean.. the only thing you can do.. Is to make an multiplayer deck itself.
Does it makes sense?