In Mario Kart World, the Coin Shell leaves a trail of coins after it is thrown.
The Coin Shell combines the familiar shell attack with a coin-collecting effect. After being launched, it travels along the course and leaves coins in its path, giving racers a chance to collect them and build speed while the item completes its attack.
The name can cause confusion because Mario Kart World also contains the ordinary Coin and the Coin Box. A Coin Box produces coins around the user, while the Coin Shell moves across the track. A Red Shell targets a rival but does not leave a coin trail, and a Golden Mushroom provides repeated speed boosts.
Coins are important in Mario Kart because carrying them increases a kart's speed, up to the game's established coin limit. The Coin Shell therefore combines offense and acceleration, making it useful both for attacking and for recovering momentum.