Screw Attack (item)
The Screw Attack made its first appearance in Metroid. In Metroid, the Screw Attack was an item that allowed Samus to attack while somersaulting. The Screw Attack also appeared in Super Metroid and it gave Samus the same ability. In Smash, the Screw Attack allows a player to do an attack while somersaulting similar to Samus' up special (which is also an attack based on the Screw Attack). The player can also double jump while holding the Screw Attack. 
In Smash, the Screw Attack resembles the one from the 2D Metroid games, but with the colors changed. It also serves as the symbol for the Metroid series.
In Melee, it can be thrown at an enemy, which forces them to perform the attack. Unlike when using it normally, however, this leaves the victim helpless in the process. When thrown, Screw Attacks can steal KOs, since the distance the character rises after getting hit by it depends on how fast the character is getting launched. If characters are launched from a high percentage and get hit by a Screw Attack, they fly up very quickly while performing the Screw Attack and often cross the blast line for a Star KO.
In Super Smash Bros. Brawl onwards, the Screw Attack is instead a badge item, similar to the Franklin Badge. As a result, it cannot be thrown as in Melee, but allows the user to attack as normal while it is being held; it will eventually fall off, however. A very large portion of the attack from Brawl onwards is interruptible, allowing it to be cancelled into any of the character's attacks. In Smash 4, the Screw Attack has a quirk of removing the character's ability to short hop while it is equipped. It also slightly boosts jump height.
Equipping the Sandshrew, Top Man, Bubbles or Helirin Support Spirits will give the player a Screw Attack at a start of a match.
One of Samus Aran's power-ups from the original Metroid, the Screw Attack turns a jump into a rotating attack move. When carrying this item, any character's ordinary jump move will turn into a Screw Attack. By the same token, if you throw this item at an enemy, your foe will spontaneously do a Screw Attack.
A badge you can wear to turn your jumps into Samus's signature Screw Attacks. In Super Smash Bros. Melee, it was an item you carried, but this time around it's a badge you wear--which means you can use it and another item at the same time. There's a good chance you'll be able to string together Screw Attacks and midair strikes for powerful combos.
This handy item grants you the same power as Samus's Screw Attack when you pick it up. With the right timing, you can execute a devastating combo of midair attacks. Be careful, though—some fighters sacrifice the height of their jumps when they're wearing this.
A badge-type item that lets you use Samus's powerful Screw Attack technique when you jump. If you use it at the right moment, you might even be able to pull off deadly combos with other mid-air strikes. But watch out - some characters' jumps might not be as high while using this.