My question was actually about your post... xD
Thanks for the info, but how would I do a setup for air DB? Is it the first hit only then a followup fair or what? I need elaboration on that part.
You could have just asked me on the discussion section on the guide post though xD
http://smashboards.com/threads/the-blade-of-two-fates-marth-lucina-guide.379525/
If there are futher question's, I'd like the conversation to be continued there please xD
Air DB in short is in one part a positioning tool for the NAir and UAir combos, and second part a means to approach (like SH FAir). The DB cuts your vertical momentum and has you stall in the air a tiny bit once it's used. Your opponent may get confused and may think you made a mistake, but then you have every air option available as well.
If you hit with the first Air DB slash, your opponent gets lifted off the ground a tiny bit. They only have a few frames to get out, and if they mess up by midair dodging or committing to a slow air move, they'll immediately land on the ground with landing lag, then they're wide open to any of your aerials (ideally NAir or UAir, as you can easily combo/setup into a number of other options). The Air DB (Particularly in SH) is actually more ideal when your opponent tries to challenge you in the air, and you connect with the first hit. They will be forced to fall with you and their options of intercepting your next attack are quite limited if you're at a sword's length away). Even if you miss, their hesitation or thinking you're open can still be punished by a FAir/BAir, or you can double jump to safety.
The ground DB setup is similar, where you lift your opponent off the ground, and it has the same quality as before if your opponent can't react fast enough. So the input is Side B > Up B > choose one of the options I listed. This one is more ideal at lower percents, as anything high like 60% and up, they will fly too far up to follow up with anything but like a chasing UAir/Dolphin Slash. At that point, you may just want to go for the regular full DB xD
Of course, weight come into play as well, as floaty characters like Jigglypuff, frame 1 moves like Ness, or fast fallers like Shiek can escape much easier than the rest of the cast. Heavy characters get abused by this pretty badly, and medium weight characters vary on results. You also need to keep in mind at what point you do the SH DB, as you can do it as soon as you jump, but it limits your choices to just the NAir/2nd DB/SB/jump options. Around half a second is the time you need to wait before executing the DB, so you have room to do any of the followups, including the ones listed to protect yourself with.
CPU's vary on whether they fall for it or make a perfect timing, and more so against human players who know the proper ways to get out of it. It heavily relies on hesitation, misinputs, and reading your opponent well. It has its flaws, but it does work. If you need the visual examples, go check the video examples section or just go to my YT page on my sig and see how it's used for yourself (granted, I taught my friends how to get out of it, so the SH DB is much harder to get on them ^^")
EDIT: Hopefully this clarifies the setup's purpose for ya. So please again, feel free to ask me any further questions you may have, I'm always happy to help
