Mafia II has its own script functions - 178 classes, about 1000 functions: how a character walks, what's in its hands, a car's plates and colour, the HUD, traffic, the weather, police... Client scripts call any of them with natives.call.
natives.call("player", "GetPos", function(ok, pos) print(pos.x, pos.y, pos.z) end)
natives.call(natives.ped(3), "AnimPlay", "sc_vito_wipe1", true) -- another player's character
natives.call(natives.vehicle(1), "SetSPZText", "M2O-777", true) -- a vehicle's plates
natives.call("game.hud", "Show", false) -- a game module
A native runs only in this player's game: what it changes, others don't see. What everyone should see goes through the server's API (that's synced).