Sonic (SSB4)/Up aerial
Sonic's up aerial is a scissor kick that hits twice, with the first hit dragging opponents above and towards Sonic for the second hit to connect. It has fast startup at frame 5, making it among the fastest up aerials in the game (losing only to Diddy Kong, Dr. Mario, Mario, Pikachu and Sheik's), and like usual moves of said type, it launches at a vertical angle (91°). Most remarkably, however, it has an extremely fast autocancel window coming out right after its hitboxes cease, making it a very low risk move useful for pressuring aerial opponents.
At low percentages, landing with this move and autocanceling it as soon as possible allows it to set up an up tilt, neutral aerial, back aerial, forward aerial or another up aerial. At mid and fairly high percents is when the move is the most useful, as Spring Jump can aid in continuing combos, but most importantly, because it gives him a deadly combo in his up throw to Spring Jump to up aerial if the former is initiated on a platform, which can KO as early as below 100%, aiding significantly in Sonic's otherwise problematic KO power.
Sonic's up aerial does have some flaws, however, which lie in its fairly high landing lag (21 frames), poor KO ability anywhere except near the upper blast line (being unable to KO under 190% at the height of Battlefield's middle platforms), and the first hit's low range in relation to the move's ending lag (24 frames), making aerial followups require good timing and an accurate prediction. The former flaw is entirely offset by its ability to autocancel immediately, however, which makes the move extremely difficult to punish, and with Sonic's outstanding neutral game, his up aerial can still be consistently comboed into for deadly effects. Due to its notable advantages overall, it is a very useful part of Sonic's aerial game and has often been considered his best aerial.
The late auto-cancel window is listed to start on frame 11 but as it is listed after the command to remove the second hit's hitboxes in the move's script, it does not auto-cancel until frame 16. It seems that the move was not supposed to auto-cancel until frame 27 but due to this error, it auto-cancels much earlier. This was carried over from Brawl, although the move auto-cancels earlier than in Brawl due to the second hit's shorter hitbox duration. The same error can be seen with Cloud's up aerial.