Add it in the same script (init to a null value), also set it whenever you get a "gamepad" Async:System event (which is triggered whenever a gamepad is connected or disconnected). It's probably easiest to handle these events by putting a persistent "gamepad connection controller"object in the first room, which is a child of parent_active (so it can't be deactivated) - then it sticks around throughout the entire game without you having to put one in every room manually.