Spiny Shell (Mario Kart)
The Spiny Shell (also commonly referred to as the Blue Shell by various media sources) is an item from the Mario Kart series. Its first appearance is in the game Mario Kart 64, in which it is known as the Blue Spiny Shell.
The Spiny Shell appears in many Mario Kart games as an item from an Item Box. Its general purpose is similar to that of a Red Shell, except that it targets the player in first place (or the leader of the race). 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.
This item has gathered notable criticism over the years, particularly with its appearance in Mario Kart Wii.
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 of first place can receive this item, but it is the rarest item in the game.
Once fired, the Blue 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 opponent or item in its path is destroyed - it 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, launching them a pretty good distance while flipping over (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 grounded, 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 hurt. 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 Luigi Balloon that will dip down with an item box on the bottom. Another is in Koopa Troopa Beach, there is a rocky hill with a lone item box on its apex with a narrow ramp before it.
Mario Kart: Super Circuit
The item serves the same function in Mario Kart: Super Circuit for the Game Boy Advance, although the shell has a darker blue color. When shot, it makes a distinct siren sound to alert those ahead that the shell is coming. 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.
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 travels.
When thrown, the shell flies at incredible speed 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 and explodes on contact. The impact causes a blue explosion (similar to a blast from a Bob-omb) and throws the player up into the air. Other racers near the leader are also blown up by the blast or spun around a bit after the impact. The blast will also 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 and so forth. Additionally, once a player holds a Spiny Shell, other racers cannot receive another shell until the player has used it and the item has exploded over its target. This rule is kept for later Mario Kart games.
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 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, creating an explosion to send the vehicle flying 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. Also, if the player was in first when the shell was 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, and has increased in size compared to previous games, though it is still able to fly despite this. Like before, it will target the leading player upon usage. Its rarity is on par with the Thunderbolt.
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 rise from the ground because of the impact; instead, they roll over uncontrollably, costing several seconds. 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, starred player, or Thunderbolt will nullify its effects.
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, zooming across the ground and taking out any players in its way. It can still be avoided by using a Mushroom, though it's harder to pull off as the item now explodes ahead of the targeted racer, get hit with another item, or by using a new item, the Super Horn, which is capable of destroying Spiny Shells in their path; however this item is very rare.  A Spiny Shell figure is also available with the Mario Kart 8 Limited Edition bundle.
Super Smash Bros. for Nintendo 3DS / Wii U
The Spiny Shell appears in Super Smash Bros. for Nintendo 3DS and is later set to appear in Super Smash Bros. for Wii U, retaining its wingless appearance in recent Mario Kart games. It flies up over one of the player's heads, falls onto them and explodes, in a similar fashion to any other explosive items. The explosion seems to be smaller than that of Mario Kart series.  The spikes can also damage opponents if the shell is below them.
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 50 coins from the leader and gives them to the user.
Names in other languages