Luigi (SSBU)/Back aerial
Luigi performs a spinning dropkick behind himself. It is Luigi's strongest aerial when sweetspotted, easily being able to K.O. at respectable percentages. Its power is also highly useful when finishing a combo. It is most useful at high percent, after a down throw, being more reliable than Luigi Cyclone on stages with high upper blast lines. At low percent, it is even able to start combos that the weaker hitboxes would be unable to after landing.
its sourspot and late hit aren't useless, either. Past low percents, when they are unsafe on hit, they can start effective combos when landing. They're able to link into all of Luigi's tilts and even his grab depending on the percent.
Because of Luigi's high jumps, back aerial isn't very useful when rising in neutral. its sweetspot is unable to hit the majority of characters when standing and the weak hit does not serve any purpose as it's not safe enough on hit. As such, it is most useful as a combo finisher when rising, a combo starter when landing and a general kill move off the stage or against opponents that are airborne.