Spiny Shell (Mario Kart)
The Spiny Shell appears in many Mario Kart games as an item from an Item Box. Its general purpose is reminiscent of a Red Shell, except that it targets the player in first place (or the leader of the race), and inflicts more damage to the targeted racer. Its function varies slightly from game to game. Aside from the Mario Kart games, the Spiny Shell is a power-up in some Mario sport games. It is easily one of the most powerful items in Mario Kart due to the random nature of its appearances, its main function of going after the leading racer, and the utter effectiveness of its attack and blast radius.
Starting from Mario Kart: Double Dash!!, the Spiny Shell is explosive, practically being the "flying" equivalent to the Bob-omb.
A Spiny Shell Collector's item is also available with the Mario Kart 8 Limited Edition bundle as well as the game disc.
Mario Kart 64
The Spiny Shell is first introduced in Mario Kart 64. In the game, the shell has spikes on it and travels along the ground. It is essentially a blue version of the common Spiny Shell. Any player outside first place can receive this item, but it is the rarest item in the game.
Once fired, the Spiny Shell will travel straight forwards for a second or two. If it hits an obstacle during this time it will be destroyed, so care must be taken to avoid wasting it. After a few seconds the shell will begin traveling along the ground, following the track ahead of the shooter. Any karts that the Spiny Shell hits will be thrown into the air. This can be avoided by moving out of the way, as it will not target anyone except the leader of the race. Once it gets to the leader, it will crash into them and disappear, sending them flying into a fairly long distance (enough to fling them over some barriers that normally cannot be jumped over). The shell makes a highly distinctive siren sound while traveling.
While it normally remains sliding along the track, the Spiny Shell will take to the air if required to continue its chase, soaring over gaps and jumps. A particularly strange case occurs on Banshee Boardwalk: the shell will fall off the edge of the track just before the house, resulting in it making a corkscrew flight to get back on. In other cases, before entering the haunted house, it can circle around the sign that says "WELCOME".
If the Blue Spiny Shell strikes an invincible racer it will be destroyed without the racer being damaged. If the leader is invisible, it will simply pass through them, though it may then simply make another lap of the course and hit them afterwards.
The shell can be dragged behind a kart like other single shells. In this position it will destroy any opposing items it touches, as well as cause opponents to crash. It cannot be fired backwards.
Using the shell while in first place will result in it turning around to hit the thrower after its straight shot.
If players get the following item boxes, they will always get a Spiny Shell. One is in Luigi Raceway, where there is a balloon that will dip down with an item box hanging on the bottom. Another is in Koopa Troopa Beach, there is a large rock with a single item box on its top with a narrow ramp before it. In the Mario Kart 7 remake of both courses, this special item box is no longer present, and is replaced by a regular one in Luigi Raceway, and a single Coin in Koopa Troopa Beach.
Mario Kart: Super Circuit
The item serves the same function as in Mario Kart 64 for Mario Kart: Super Circuit for the Game Boy Advance, although the shell has a darker blue color. Like before, it makes a distinct siren sound when traveling. Like the Red Shells in the game, it can be dropped behind the player and will activate only if the kart in the first position passes directly by it. The Spiny Shell is also easier to avoid; if the player jumps over an abyss or over a previous section in the track (like the jump in Mario Circuit 2) the shell will fall in the abyss or crash into the wall.
The impact of the Spiny Shell no longer cause the leader to crash and thrown off, instead they will spin out and stop in the spot he or she was hit. This trait is later reused in Mario Kart 8.
Mario Kart: Double Dash!!
In Mario Kart: Double Dash!!, the Spiny Shell is changed significantly. It is a standard item that any player in fourth place or lower can obtain. In this game, the shell appears with a pair of wings that allows the item to fly instead of sliding over the ground, which lets it skip any obstacle found in the course. The shell now makes a hissing noise as it launches.
When thrown, the shell flies at incredibly fast speeds to the current head racer, bypassing all of the other positions. After finding its target, the shell hovers over the vehicle to home in on it. Double Dash!! is the first game where the Spiny Shell explode on impact and throws the racer up into the air, also causing their kart to backflip. The blast is similar to a Bob-omb, except that it's colored blue and somewhat larger. This trait is kept for subsequent games.
Other racers that caught in the explosion will spin out and cause all the items held by the player to drop to the road while destroying any items already on the ground.
The Spiny Shell always goes for the leading player in the race (even if it is the shooter). Therefore, if the player in first already crossed the finish line, any Spiny Shell shot after that point will go to the active leader of the race (in this case the second-place racer). Thus, once the player in second crosses the line, the shell will target the player in third, and so on. Additionally, once a player holds a Spiny Shell, other racers cannot receive another shell until the player has used it and hit the target. This rule is kept for later games as well.
To avoid the Spiny Shell, the player has multiple possibilities. He or she can either use a perfectly-timed Mushroom, use a Star to make the item completely harmless, or by skillfully performing a Mini-Turbo by drifting, which will sometimes cause the Spiny Shell to spin around the player and crash into a wall.
Mario Kart DS
In Mario Kart DS, the Spiny Shell has not changed since its redesign in Mario Kart: Double Dash!!. The Spiny Shell works in the same manner as in Mario Kart: Double Dash!!. It is obtainable from fourth to seventh place. Once fired, a Spiny Shell flies following the road to reach to the leader. Once locating its target, the shell flies around briefly over its target and falls over the vehicle before exploding on impact, sending the vehicle thrown upwards and destroy the items held by the racer. Almost unavoidable, a player can avoid the explosion by using invincibility items like a Star, a Bullet Bill, or Boo. Tumbling as a result of getting hit by something like a Fake Item Box will also prevent the damage received by the explosion. Finally, the shell can be avoided by skillful use of a Mini-Turbo; karts with a high handling (like the Dry Bomber) can do it by a timed hop right after releasing the Mini-turbo.
Mario Kart Wii
The Spiny Shell makes an appearance in Mario Kart Wii for the Wii. Its function is identical to Mario Kart: Double Dash!! and Mario Kart DS, and it can be obtained if the racer is between fourth and eighth place.
If a player is targeted for attack by a Spiny Shell or is in the vicinity to be hit by the blast, the player can avoid the attack by means of a Star, Mega Mushroom, Bullet Bill, well-timed Mushroom, or by passing through a Barrel Cannon or the Launch Star found on Rainbow Road. It is even possible to drop a Banana at a very precise time during the drop after a jump, which causes the Banana to collide with the shell and spare the target. Doing a trick off a ramp at the perfect time can also result in avoiding a Spiny Shell. Also, if the player is in first when the shell is fired and drops out of that position, the shell will still attack that player.
In team play, the Spiny Shell will aim for whoever on the opposing team is farthest in front, ignoring and not damaging anyone on the user's team (so it will target the racer in fourth if the first three racers are on the user's team). For the first time, the item is also available in Battle Mode, flying straight to the opposing team's highest-scoring player after a short delay. The shell is much rarer in Battle Mode than Versus Mode and only appears if there is a very large score difference between the user and the leader.
Mario Kart 7
The Spiny Shell makes its appearance in Mario Kart 7. The shell is now wingless, like its first incarnation, has increased in size compared to previous games, travels on the ground, and it will only fly when alnost reaching its target. Like before, it will explode on impact with the leading racer, but this time will also hit other racers in its way whilst sliding across the ground. Its rarity is on par with Lightning. The explosion is also less effective than in past games.
All of the racers hit by the shell drop Coins, but those hit by the explosion may also lose the items that they were armed with. Unlike in Mario Kart Wii, the racers in the front hit by the Shell's explosion do not thrown off the ground. Instead, they crash and roll over sideways. The impact can be dangerous on course where it's possible to fall off, such as Rainbow Road.
The Spiny Shell cannot be avoided unless the player uses a Mushroom, a Star, or a Bullet Bill, drops out of first place before the item is launched, or falling off the course. Even being hit by a perfectly-timed Shell, Banana, invincible racers, or Lightning will nullify its effects.
It is now also have a new and different sound, which is the louder, low-pitched variant of the Green Shell sound.
Mario Kart 8
The Spiny Shell returns in Mario Kart 8. It once again has no wings but has a darker, royal blue color. It mainly acts like it does in Mario Kart 7, but this time it flies low over the ground and travels slightly faster, about as fast as the one in Mario Kart DS. Like in previous games, it can be avoided by using a Mushroom, though it is harder to pull off as the item now explodes ahead of the targeted racer. It can also be avoided by getting hit with another item, or by using a new item, the Super Horn, which is capable of destroying Spiny Shells in their path; this item, however, is very rare.  Spiny Shells also cannot travel further than a set distance: if they exceed the distance, then the shell will disappear. This can easily be demonstrated by playing on N64 Yoshi Valley, where the Spiny Shell can easily miss the player if it takes the wrong path as the player and continue on its path, and it will not go another lap in attempt to hit the player again.
It is also much less powerful in this game, with the explosion now only stops the target in the spot he or she was hit, instead of causing them to crash. This is notably similar to that of Mario Kart: Super Circuit.
Due to the new item system (where it mostly depends on distance from the front runner), it is possible to get the shell from any place other than first.
In addition, the shell's sound appears to be a combination of Mario Kart 7 and previous games.
Super Smash Bros. for Nintendo 3DS / Wii U
The Spiny Shell appears as an item in Super Smash Bros. for Nintendo 3DS / Wii U, retaining its wingless appearance in recent Mario Kart games. It hovers over the leading player (or the second-scoring player if the leading player has thrown it), and after a while, falls and explodes. Its fall speed varies, giving the target more or less reaction time to dodge. In team battles with friendly fire off, the Spiny Shell attacks the leading player in the opposing team, although with friendly fire on, it targets the leading player regardless of team affiliation. The explosion seems to be smaller than that of Mario Kart series. The spikes can also damage opponents if the shell is below them, and when it is hovering overhead.
Mario Hoops 3-on-3
In Mario Hoops 3-on-3, the Spiny Shell is known as "Angel Shell", and its appearance is similar to its appearance in Mario Kart 64. The shell is a homing projectile that once thrown, chases the basketball in play and explodes upon contact in a similar fashion to a Bomb. The resulting explosion damages all players.
Mario Superstar Baseball
The Spiny Shell appears as an item in Toy Field. It steals fifty coins from the leader and gives them to the user.
Super Smash Bros. for Nintendo 3DS / Wii U Trophy information
Blue indicates exclusive to the Wii U version.
Names in other languages