Stingler

The Stingler is an item used in Mario & Luigi: Bowser's Inside Story. There is only one Stingler, which appears in Pump Works. While Mario & Luigi are searching for the Princess, they discover a door with a odd key slot. Later, they find this item, and it turns out that this is the item they need to enter through the door. Once returning to the door, they slide in the stingler into the door. That activates more sections of Bowser to appear, including the Flame Pipe where it is believed the Princess may be at.