Pick up bag of coal and hammer. Place coal onto top of furnace. Drag torch to heat up coal. Tap fan inside furnace repeatedly until room smokes up.
Shake your phone to clear out smoke. You can do this every time the room smokes up.
Drag the three rocks around the room to where you placed the coal (one rock on left shelf, one rock on top right ceiling, one rock to right of anvil).
Drag small black piece of key mold to pile of rocks on coal (black mold found on bottom left corner of furnace).
Complete the key by dragging the four pieces into place. Drag your hammer in your inventory to hammer out and make the key.
Finally, use the metal holding tool to grab the key and place into the water bucket to cool.
Pick up the key and use it to escape.
Proceed to the next level!