The Spiny Shell (トゲゾーこうら, Spiny Shell), popularly known as the Blue Shell, is an item from the Mario Kart series that appears in Super Smash Bros. 4 and Super Smash Bros. Ultimate. First seen in the April 2014 Nintendo Direct, it functions as a thrown item which launches a delayed attack on the leading opponent of the thrower.
This item appears to be the most common variation of a Spiny Shell in Mario spin-off games including the Mario Kart series. It originates from Mario Kart 64, where it appeared as an incredibly rare item from an Item Box that would tear through the track in pursuit of the racer in first place, to whom it would deliver a massive blow; it would also bash through any other racers and items that happened to be in the way. It is one of the most notorious items in the series, stalling the target for an extremely long time and being nearly impossible to avoid once thrown, even when predicted. Later games in the series gave the shell wings, so it flies straight to the leading racer without making contact with other racers, and a large explosion upon touching down on its target, with a blast radius large enough to catch surrounding racers as well. In modern games, it still explodes upon hitting the leading racer, but it lost its wings, and is thus able to hit racers that happen to be in its path like before. Its design in Super Smash Bros. 4 and Super Smash Bros. Ultimate is taken from its appearance since Mario Kart 7.
Due to hitting the player in first place, the Spiny Shell is notorious for being one of the most, if not the most, dreaded items in the Mario Kart series. The only way to stop it is with the Super Horn, which was introduced in Mario Kart 8.
When thrown, the Spiny Shell targets the current highest-ranking opponent of the thrower - the one with the most points in time matches, the most stocks in stock matches, or the most coins in coin matches. If multiple opponents have equal standing, the one with the least damage is picked, and if multiple opponents also have equal damage, the one closest to the thrower is picked. The Spiny Shell flies to and hovers above its target, continuing to follow above them for five seconds, and then slams down onto said player. The Spiny Shell explodes upon hitting an opponent or other hurtbox during its attack, which deals 28% damage with sizeable knockback. The time it takes from falling on its target to exploding is randomized, which can potentially make the attack difficult to dodge.
When the Spiny Shell is slamming, its explosion triggers as soon as it hits a player or hurtbox. Hence, it is possible for the Spiny Shell's target to avoid its attack by hiding under other players, so that another player takes the hit of the Spiny Shell. If the player being targeted is KO'd before the shell can attack, it will explode on the spot without trying to target anyone else.
While the Spiny Shell is flying and hovering, opponents making contact with it will be hit for light damage. This can potentially force an opponent other than the target to be hit by the shell's explosion attack if they are trapped by the hovering hits.