Shuttle Loop (シャトルループ, Shuttle Loop) is Meta Knight's up special move. Meta Knight jumps into the air with his sword pointed upwards, goes into a loop, and in Brawl, glides forward with his blade extended. In Super Smash Bros. 4, however, he follows up with a second swipe instead, due to the removal of gliding in Smash 4.
In Super Smash Bros. Brawl
The Shuttle Loop does 9% damage, and has good knockback, making it one of Meta Knight's finishing moves. Meta Knight's grounded Shuttle Loop has vertical knockback and invincibility frames at the beginning of the move, while the air version has strong horizontal knockback, being a solid edge-guarding move due its high base knockback. The initial upswing of the Shuttle Loop is mostly used at the end of Meta Knight's combos.
It should also be noted that the end of the Shuttle Loop attack automatically initiates a glide, which can be used in addition to the vertical recovery to add good horizontal recovery. In addition, because Meta Knight can do a quick attack to conclude a glide, Shuttle Loop can be timed to do two consecutive attacks - the initial upswing, and the quick swing from the glide. The glide from this attack is slower than his regular glide, and allows better control.
Using Shuttle Loop while facing off of the edge can be quite dangerous, for unless the player quickly cancels the glide, he/she could easily glide right off the stage with no chance of recovery. Also, landing while in the glide puts Meta Knight on the floor, and the opponent can easily punish him. Using his glide attack or just pressing the special move button right before hitting the floor completely cancels the attack and landing lag, which leaves him in an ideal position to evade attacks or hit opponents.
In Super Smash Bros. 4, the attack no longer cancels into a glide due to the removal of gliding; however, it gains slightly more vertical distance and causes Meta Knight to do an extremely quick double loop, causing it to hit twice. The move now does a total of 15% damage (12% in the air) and retains its high base knockback from Brawl, still making it a viable finishing move, especially as part of the Rufio combo. Despite the removal of gliding, the aforementioned increase in vertical distance still makes the move good for recovering, especially due to Meta Knight retaining his excellent aerial mobility.
Special Move customization was added in Super Smash Bros. 4. These are the variations:
The move is similar to one of Wing Kirby's attacks with the same name. It was used by Kirby in Kirby Super Star when he received the Copy Ability. The only differences are that it didn't make Kirby glide and it lacked the sword. In addition, the Wing ability's attack required the player to toss an enemy first. This makes it more similar to its SSB4 incarnation than its Brawl incarnation.
Meta Knight also uses this move in later Kirby games, including Kirby's Return to Dream Land, Kirby: Planet Robobot, and Kirby Star Allies. It functions differently from Wing Kirby's version and identically to its Brawl incarnation, sending him into a controllable glide. The move is also similar to one of his attacks as a boss, where he jumps backwards and quickly dives forward with his sword.