The Spiny Shell, also known by many names (such as the Blue Shell, the Blue Spiny Shell, the Blue Terror, the Blue Menace, the Leader Killer and the First Place Stalker) is an item that has appeared in every Mario Kart game except for Super Mario Kart, though it has taken different forms between games. The shell has a distinctive dark blue surface with spikes on top. Depending on the game, the shell may or may not have white wings. It is hated by many people, and can prove the deciding factor for who wins and loses a race, as many an unfortunate victim have learned the hard way. Because of how much hate this item receives, many people consider this item to be the WORST Mario Kart Item.
While devastating, the Spiny Shell is not entirely unavoidable, as it can usually be avoided by using a Mushroom with proper timing, among other speed-altering maneuvers. The Super Horn, introduced in Mario Kart 8, can also be used to block the Spiny Shell from connecting.
In earlier games
In Mario Kart 64 and Mario Kart: Super Circuit, the Spiny Shell will travel along the middle of the track until it hits the racer in first place, knocking out any racers in its path along the way. The imminent impact of a Spiny Shell is signaled by a siren, giving the first place driver time to anticipate the shell with an item or bait the second place driver into the lead to take the punishment. Unlike in future games, the Spiny Shell will break if fired at a wall and is not able to clear some larger jumps. As the shell cannot be broken by other items or racers, many players find it extremely useful to hold the Spiny Shell behind them indefinitely, thereby protecting them from any items or racers approaching from behind. The only way for the first place racer to avoid being hit by the shell is to use a Starman or Boo. Players between the leader and the racer who fired the shell can simply move away from the middle of the track to avoid being hit. Like the Red Shell, in Super Circuit, the Spiny Shell can be planted on the track and used as a homing device, though this does not exercise the full brunt of its potential to take down a pack of racers. However, it can be used as an alternate strategy for a last place driver to plant the shell somewhere that will take out the leader as they pass by, without the worry of anyone prematurely attracting the Spiny Shell.
Mario Kart: Double Dash!! to Mario Kart Wii
In Mario Kart: Double Dash!!, Mario Kart DS, and Mario Kart Wii, the Spiny Shell's appearance and behavior have been changed. The shell no longer travels on the ground while hitting other players; instead, it will quickly fly above the track directly towards the first place racer. Since it flies, it is able to cross large jumps and ignore walls and other obstacles. The shell does not "lock-on" to a target until it is near the front of the pack. In other words, if the racer in first place at the time of firing drops back to second place, the shell will instead target the new leader. However, if the shell is already near the front of the pack, then it has probably already locked onto a racer and will target them even if they drop back. Upon arrival, the shell will hover over the leader for a moment and then suddenly smash into the ground, resulting in a large blue explosion, comparable to a Bob-omb's, that knocks out any racers within the blast radius. The Spiny Shell's characteristic hissing sound serves both to alert the first place racer of their impending demise as well as to warn nearby racers to stay clear of the blast zone. In Double Dash!! and Wii, the only way to avoid these shells is by using an item that grants invincibility, boosting with a mushroom, or hopping into a cannon at the right time. In DS on higher engine classes, the Spiny Shell can actually be avoided by readying a Mini-Turbo and releasing it with precise timing as the shell is about to hit, although this is quite difficult to consistently perform. Mario Kart Wii is also the first (and so far only) time where the Spiny Shell has appeared in Battle Mode. Here the player it goes after depends on the type of battle. In Balloon Battle, the Spiny Shell goes after the player with the most hits whereas in Coin Runners it will go after the player with the most Coins. Due to the fact that MKW battles are always locked onto teams, the Spiny Shell only goes after the member of the opposing team who's doing the best.
Mario Kart 7 and Mario Kart 8
In Mario Kart 7, the Spiny Shell has received a slight change of behavior, taking its design from Mario Kart 64 and Mario Kart Super Circuit, because of having no wings. It is now a combination of the two preceding types of Spiny Shell- it floats in the air and homes in on the first place racer (similar to the more recent versions,) but is only slightly above the track, allowing it to smash into other players on its path (similar to the original version.) Upon reaching the first place driver, it will float in the air directly above them and smash into them, causing a blue explosion that also harms adjacent drivers within its blast radius. Unlike in previous games, the explosion does not send players straight up; rather, it sends players tumbling sideways, which is arguably more dangerous as it opens the opportunity for a player to fall off the track much more easily than any previous incarnations, slipping them behind even more. It can also now hit players traveling through cannons in courses such as Maple Treeway or DS Airship Fortress, sending them to an unavoidable plummet with twice the coin loss and likely several drops in position. The only way to avoid this Spiny Shell is to use invincibility or speed-boosting items such as Stars, Mushrooms, and Bullet Bills, or to quickly back up as soon as the dreaded icon appears next to a player on the minimap.
In Mario Kart 8, the Spiny Shell retains its wingless form and still have the same functions from the previous games: flying towards the first-place racer while knocking over any racer along the way (from Mario Kart 64, Mario Kart Super Circuit, and Mario Kart 7), as well as creating an explosion upon impact that spins out any nearby racers within the blast zone (from Mario Kart: Double Dash!!, Mario Kart DS, Mario Kart Wii, and Mario Kart 7). This item is unbreakable as in all of the previous games. However, the newly introduced Super Horn item can destroy the Spiny Shell, take that Spiny Shell! It can also be avoided with a perfectly timed mushroom boost or invincibility, as with previous games. The Spiny Shell has been nerfed in this game as it doesn't send the targeted players sky high or tumbling sideways but rather briefly stuns them on the ground. However, the Spiny Shell is still able to hit players when they are in glider mode or have exited out of a launch cannon.