Question: how to get the key in the cage lift room in luigi's mansion 3?
Answer: Walk Luigi over to the chest to get the key. Return to the Cage-Lift Room, take out the ghosts that appear and then open the bottom right door to enter the Dungeon. In the Dungeon walk to the left and have Gooigi pull the ball on the wall here to open the cell. Send Luigi into the cell and grab the key.