Is it commonly known that you can fake drop-through, on moving platforms (AKA, those than can be platform cancelled on) by tapping down and then C-sticking down? I was playing around with platform cancelling and related things, and I noticed this - I couldn't find it in the AT thread, so I figured I'd inquire here. It seems to be lag-free as well.
And, after some further testing (I initially was just using Marth to mess around with this), it seems like not all characters function the same way. I only tested the top row of characters, but of them all but G&W and Pika worked the same as Marth. G&W and Pika both executed an instantaneous Dair on top of the platform, dealing damage and etc. as usual. The timing on G&W was about the same as the other characters, but the height that his Dair started at varied a little with the distance between the input of down and C-Down. If I got it just right, it seemed to cancel altogether, but the timing was quite a bit trickier than the others. Pika, on the other hand, required tricky timing just to do the Dair, and had no variety in the height of it. It seems like maybe characters with Dairs that add downward momentum act differently...and perhaps the fall-then-stall mechanism accounts for the change in G&Ws height.
Edit: Stall-then-fall does seem to be the factor that messes with this. Also, you can perform this by holding down and pressing A - by doing this, you can also have a little more control over how much of the drop-through animation occurs before cancelled, and you can also continue to hold down after the cancel to crouch/perform Dtilts. It's a little trickier, though, than C-Sticking it. The timing is just slightly slower than a Dsmash, and down should be held for just a tiny bit longer than if you just flicked it down.