The Red Shell (a red Koopa shell) is a throwing item appearing in the first two Super Smash Bros. games that actively hunts out the nearest player, even the player that activated it. Instead of sliding in the same direction it was thrown in after coming in contact with the ground, it starts sliding from left to right, targeting the closest player. When stationary, the Red Shell activates when jumped on or after coming in contact with a hitbox. Like the Green Shell, a sliding Red Shell halts all movement upon being jumped on. The Red Shell does moderate set knockback. When the Red Shell is reflected, its damage output is increased, but its knockback is not. A reflected Red Shell will also have much more hitlag when it hits a player.
The Red Koopa Shell is a special item that appears in the Adventure Mode of Melee and in The Subspace Emissary of Brawl, which can only be obtained by attacking a Red Koopa Paratroopa or Red Koopa Troopa. Although similar (but not identical) in appearance to a Red Shell, it behaves like a Green Shell, and does fire damage in Melee. When compared to the Green Koopa Shell, it does even more damage and knockback. Another difference from the Red Shell is if it is left alone for a while, it will turn back into a Red Koopa Troopa.
Throw a Red Shell, and it will home in on random characters and send them flying straight up. Red Shells moving around the surface are dangerous to all players, but they may also present attack chances for players with good timing and strategy. Red Shells won't leave the platform they're on once they start moving.
The behavior of a thrown Red Shell in the games is similar to that in the Mario Kart series, in which Red Shells' home into the nearest opposite driver running in front of the player who uses it.
The Red Shell is the only item or projectile in Melee that doesn't deal more knockback when reflected. It does, however, deal more damage.
In the first stage of Melee's Adventure Mode, the player will earn the Dead-Weight KO bonus for each Yoshi they KO with the Red Koopa Shell.
The fact that the Red Koopa Shell won't leave the platform it's thrown on is a reference to the behavior of Red Koopa Troopas in the Mario Bros. series, who, unlike Green Koopa Troopas, will not walk off of the platform they are on.
In the original Super Smash Bros. training mode, if four red shells are spawned in the same spot, and if Ness uses PK Fire on them, they will do about 460% damage upon contact.