(Prepare yourselves for a long post XD)
Unfortunately DTL, it won't happen because the part that would be able to cancel is the part where Toon actually bobs up. But, you did give me an idea. And it worked.
I actually got the Dair to cancel. Many times. So I have proven that it is theoretically possible to cancel the Dair. But how did I do it? Well as I just said to DTL, the Dair can't be cancelled normally because Toon bobs up at the start, so I simply made him not bob up by using momentum. When Toon Dairs while he has momentum, he won't bob up, he'll simply slowly fall.
So to re-create this yourselves, go to training, pick any character, make the cpu Toon, (grab two controllers), Go to Battlefield, using P1 put the cpu on control with the percent at 154% and make the speed 1/4 so you can see the cancel clearer and so the whole thing is easier. Now taking P2, make Toon stand under one of the bottom platforms, pull out a Bomb, hold down, throw the Bomb at your feet (still holding down) and then start spamming A (resulting in a Dair as soon as possible) (If your going to spam A really fast, then you might want the percent at 153%).
What will happen is, you'll blow yourself up, Toon will Dair for a split second and it will auto cancel on the platform without the shockwave like affect. (Holding down simply makes things easier, it does not affect the auto cancel.)
But wait there's more. You know how I said that if you're going to spam A really fast then you might want the percent on 153%? Well, I had the percent on 154%, I spammed really fast, and normaly this will result in the shockwave like affect and it won't auto cancel. But something else happend to me twice, where I was on 154%, I spammed, and the Dair landed right on the edge of the platform. Toon landed on the edge of the platform for a split second resulting in the shockwave like affect, and then I slid off the platform and it Auto cancelled into another Dair. So this means that I have solved the case of Copacetic's Dair that cancelled on the edge of the platform. I can finally say that this is confirmed. It is possible. What's more I can tell you how it happened, more or less. It was as I thought, the momentum of the MK's neutral B made you slowly fall a Dair right near the edge of the platform, it didn't auto cancel the normal way otherwise you wouldn't have seen it, rather it auto cancelled a second way, so you were a little bit higher up then the first way and the Dair landed on the edge of the platform (so you had actually landed at this point but you still had a bit of momentum) then the momentum and the fact that you were right on the edge, slid you off. At this point you had auto cancelled the Dair, the second way, and were able to Bair before you touched the ground.
So there are two types of auto canceled Dair (so far).
The first way, monentum stops the Dair from bobbing up and you Dair right when you are level with the platform. There is no hitbox. The Dair animation is only out for a split second.
The second way, momentum stops the Dair from bobbing up and you Dair right on the edge of the platform. You actually land on the edge of the platform for a split second, so I'm guessing that there is a wind box and the strange hitbox of the Dair Shockwave. Then the momentum plus the fact that you're right on the edge, pushes you off the platform resulting in an auto cancel.
Unfortunatelly, I still don't know how Sasuke's one works.
Now I know that this is extremely situational and because of that, it's not very useful, I'm not trying to make it out to be useful. All I'm saying is that for the first time ever, it has been proven that the Dair can in fact cancel, in two known ways. It is possible. Now we've just gotta find a way to make it more useful and less situational.
Fox Is Openly Detective, has solved the case XD.
Edit: So I found a really easy way to re-create the second version of the auto cancelled Dair. Same thing as before, cpu Toon, control, you can do it easilly in normal speed so don't bother putting it on 1/4, put the cpu's percent to exactly 82%. Right, get Toon to stand on top of the right platform, pull out a bomb, walk over to the right side of the right platform until he does that thing where he waves his arms about (the very edge), Hit and hold down to make Toon fall through the platform, (still holding down) spam A. What will happen is Toon will fall through the platform, throw a Bomb down and be hit by the explosion, slowly fall a Dair and will always land on the very edge of the left side of the right platform (Unless the Bomb blows you the wrong way, in which case your throwing the bomb down too early, I think). You will see the shockwave, then the Dair will always cancel and you will be able to Instantly use any aerial (Including Bair. Copacetic's thing.). This is fun stuff.
Also, because I found a way to use the second version consistently, I was able to do a few tests. For that split second, the Dair that is cancelled has a wind hitbox (so you can push stuff laglessly XD) and the spike hitbox of the Dair. So if someone interupts the Dair before you reach the platform, they will be hit with the spike hitbox (Possibly a way to safe spike laglessly? I'll keep checking stuff out.) Get this though, it doesn't have the Dair shockwave hitbox because it cancels too early and the Dair shockwave hitbox comes out slightly later. Oh well.
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