Luigi (SSBU)/Down smash
Luigi sweeps around himself with both legs. While being his weakest smash attack, it is also by far his fastest, with the first hit coming out on frame 6, with a frame 14 second hit. It has a sweetspot on both hits on Luigi's hip, reliably killing at ~140%, which also have priority over the sourspot. The move causes Luigi to go low, allowing him to low-profile aerials and catch landing attempts easier, while sending at an alternative angle to up smash which can switch up the opponent's DI. It is also possible to use down smash out of a run turnaround, in order to get both hits to hit shield, which leads to good shield damage, which can be useful as an unexpected shield-break method.
Down smash's back hit, despite possessing a weaker sound effect, has more knockback scaling over the first hit, which also makes it very effective against rolls. It is also able to hit ledgehang animations, however down tilt is usually preferred due to being less committal and hitting every ledgehang in the game as opposed to down smash. With its speed and range, it can make for a decent punish for when Super Jump Punch is unable to reach.