Meta Knight (SSB4)/Down smash
Meta Knight slashes around himself while spinning. In terms of start-up and hitbox intervals, it is the overall fastest smash attack in the game, and has decent range. It is tied with his down aerial for the fastest semi-spike in the game, with the first hit coming out on frame 4, giving very little chance to DI and segueing well into his potent edge-guarding ability. The second hit is considerably stronger, KOing at around 110% near the ledge.
However, the first hit has very low power, and the move has high ending lag. Meta Knight has other attacks capable of putting opponents offstage while not carrying as much risk, most notably his down aerial and back throw. As such, down smash is best used for relieving pressure in tight situations.