Blue shell

The spiny shell, commonly referred to as the blue shell, is a well-known power-up item of the Mario Kart series of video games. Originating in Mario Kart 64, it allows a racer to shoot a projectile directly at the first place racer. The blue shell acts as a "catch-up" system, intended to give the lower-ranking characters a better chance to advance, keeping players closer together. A character in first place is likely to be hit by a blue shell at some point and once fired, the blue shell is almost always unavoidable. Because of this, the power-up has received a very mixed reception.