I'm pretty new to the Competetive Smash-scene, even though I have been playing Melee much as a child and played Brawl alot, so it might already be a known Luigi thing, but I'll bring it out there in case it isn't.
While practicing my Luigi the other day I discovered something funny. When dropping off any platform you can sweetspot a jump and skip the jumping animation to instantly land ontop of the platform. This can lead to quick ground-based moves and can be quite surprising. I'm now trying to incoporate this into my playstyle and have tried a few combos with the technique.
One of the coolest things about this technique is when Shield dropping through the platform, jumping and Shield Grabbing instantly when landing on the platform as shown in the video. After the grab you thrown up or down and follow up with an Up + B for a low percentage kill on certain stages if you're standing on the highest platform!