Was chatting with Vicegrip about something Ive known for a while but it seems a lot of people might actually not know about it all.
If you land on a platform or stage at the peak of your upb height, youll land with mere landing lag it appears and can go straight into a jump started cart dash, upsmash, etc.
The spacing/timing can be difficult at first, as well as holding down for a mere moment when youre landing on stage, as to prevent ledgesnapping. But all in all once you have it down, it seems like it can be a really nice surprise tool to catch people off guard, especially combined with cart dash.
if youre practicing consistency, if youre on the edge: tap back to let go, upair, and begin fast falling a little ways into the attack. then UpB asap and it should set you at a good distance for it to cancel. On stages like BF, you can generally let go of the edge, toss an upair, and upb and land on the nearest platform and have it cancel perfectly, as long as you dont really touch the edge of the stage much as your passing it on the way up.
Another interesting bit of info involved using mechakoopas. we can actually still get them to bounce on the stage out of an aerial toss. in a good amount of frames just before landing from the air, you are able to throw a bounce-able mechakoopa downward and itll still bounce up as long as it doesnt hit anyone. ( including shields, i believe)
One last thing involved aerial spinout and sliding afterward vs spinning in place on landing. the window is relatively small but if you use a reliable height reference it seems you can get it down pretty consistently given the circumstances. For me, I've found that if i spinout at a height above the ground where I would theoretically hit Mario in the face/head with my tires, i will spinout in place. there is a little bit of room for fluctuation, but pretty much anything too far above or below that will give you the slide it seems. Trying in training mode vs different characters and finding the window yourself can be very helpful, but all in all it seems like its one of those things you just have to get down consistently. but i am pretty certain that whether or not we slide depends on the height at which we spinout..