Shuttle Loop (シャトルループ Shattoru Rūpu) is Meta Knight's up special move. Seen in this screenshot and in a few videos posted outside the Smash Bros. DOJO!!, Meta Knight jumps into the air with his sword pointed upwards, goes into a loop and glides forward with his blade extended. The Shuttle Loop does around 9% of damage, and has good knockback, making it one of Meta Knight's few finishing moves. The ground Shuttle Loop has vertical knockback and invincibility frames at the beginning of the move and 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, the 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.
One should be careful when using Shuttle Loop while facing off of the edge, for unless they quickly cancel the glide, the player 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 the Glide Attack or just pressing the special move button right before hitting the floor completely cancels the attack and landing lag, leaving him completely ready to use any move or evade an incoming attack that would have otherwise hit him.
 Description from the Instruction Booklet
Jump and flip in midair, then glide forwards.
Shuttle Loop was used by Kirby in the SNES game Kirby Super Star when he received the Wing 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.
 See also