Wario Land 3: Part 40: The Pool of Rain (Blue Chest)

There is a glass container in The Pool of Rain that was raised by getting the Air-Pump from The Colossal Hole's Red Chest. This reveals an underwater doorway that Wario can enter in this level. Beyond that doorway is a room that contains both the Blue Key and Blue Chest. You must first head to the right while avoiding the enemies that can turn you into Puffy Wario to reach the Blue Key, then lead one of those enemies to the left and let it turn you into Puffy Wario to reach the Blue Chest. The Pool of Rain's Blue Chest Treasure is the Yellow Crayon, which colors in the 'GAME' sign of the building Wario keeps passing by between the North and West sides of this world.