for (var/client/c in locate(1, 1, 1))
world << "Loc."
Problem description: I use the above code and as I test multiplayer, it doesn't print even if another client player is in (1, 1, 1) position. If I replace however var/client/c with var/mob/player then it works...
You can loop through the mobs instead, and check if they have a client, if(player.client)