Don't know how often it has been discussed, but short hop down air has an interesting use in edge guarding. The spike hit happens frame 34, which is exactly 1 frame before Lucas lands from his short hop, making it easy to time when trying to hit someone recovering under a stage with a thin ledge (such as Battlefield and Lylat Cruise--although the tilt on Lylat Cruise can mess with the rather frame-perfect timing of the move). Think of how Falcons try to dair people through stages, or ZSS using her down b kick to hit through ledges. That kind of thing. If you want to see just how far down it reaches try it on Battlefield (WiiU) or Pac-Maze (3DS; the ledge on the 3DS version of Battlefield is actually pretty thick, so it's harder to see than in the WiiU version).
Also on the topic of down air, at early percentages where dair doesn't have strong spiking potential (only 5% damage with 10 base knockback, so it's a rather large window) it CAN put you in position where you can footstool the opponent as you fall with them after the hit, much the way Kirby players use fast-fall dair to footstool, but much trickier since you're relying on hitting the opponent with a frame 34 hit that spans a total of two frames. I think it only works on a strange percentage window, though, since if you do it too early the final hit doesn't have enough hitstun for you to follow up with the footstool, but too high of a percentage can put them too far down for the footstool (although that may mean your opponent is losing a stock anyway).
Pretty situational stuff, but worth mentioning, I think.
, but I'm not sure...
