Ah ! Another question while I'm here : the multiplayer objet can sync instances positions and variables.
So, what's the best way to synchronize attributes like visibility ?
Send a broadcast message to the peers, the peer receives it and changes the instance visibility ?
Or just to add an instance variable "visibility" on the object which will synchronize automatically, and add a global event (availble for the host and peers) like "if sprite visibility = true -> sprite ; set visible" ?