Sheik (SSB4)/Forward aerial
For her forward aerial, Sheik leans forward and slashes in front of her with one hand. This is notably one of Sheik's most commonly used moves in high level play, and is often considered the best forward aerial in the game. It is very safe to use thanks to its great range, fast startup, low landing lag, quick interruptibility and most notoriously its extremely early autocancel window, which comes out just 3 frames after the move's hitboxes cease. Thanks to all these properties, it can can combo into itself multiple times, a neutral aerial or Bouncing Fish to rack up damage and edgeguard offstage opponents. It deals more damage when hit with the sweetspot, dealing 5% instead of 4.3%.
Interestingly, despite being interruptible on frame 35, Sheik's forward aerial actually has an extremely long animation, taking 86 frames to complete. While this has minimal effect in regular gameplay due to its aforementioned interruptibility and low landing lag nevertheless, it prevents Sheik from grabbing ledges for a long time after using the move, requiring her to land on the stage or grab the ledge with Vanish instead. 
Sheik's forward aerial has been nerfed in game updates. Both patch 1.0.4 and 1.1.0 reduced its damage output, with the latter also having made its sourspot override its sweetspot. While this allows it to combo into itself even better due to less damage resulting in less knockback, it drastically weakens the damage racking ability it previously had, which is further hindered by stale-move negation as a consequence of the move being used often. Patch 1.1.5 additionally decreased the move's range, making it less effective for spacing. Because of these changes, while still being used very prominently due to its low lag, Sheik's forward aerial is largely worse than it was in the original game.