Sonic (SSBU)/Up aerial
A scissor kick. Its very large auto-cancel window makes it deceptively safe and easy to avoid even its fairly low landing lag. In addition to being a reliable follow-up from Spin Dash, Spin Charge, and Spring Jump-assisted combos, it is a viable KOing option near the upper blast line, especially as a follow-up from Spring Jump. Both hits don't always connect very reliably however. Despite this, the move still possesses good combo potential should the second hit land. It also has the lowest start up (tied with forward aerial) of Sonic's aerials, coming out on frame 5.
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. This was carried over from the previous two games.