I'm going to go on record and say that ASC u-smash isn't as hard to do now as some people are making it out to be. I've only missed two since the patch went live: the first one was because my opponent was too far behind me for the hitbox to connect (should've d-air'd instead for more damage; the u-smash probably wouldn't have killed at the % my opponent was at anyway), and the second one was because I got hit by a luma that was returning to Rosa before the second, strong hit could connect. I went to a weekly this last Thursday and landed at least 6 ASC JCUS for kills, 4 of which were in bracket matches, and the rest were in friendlies.
ASC b-air is the real problem. It's a lot more % specific, but you can still hit tall and/or floaty characters with it. I managed to get Rosa at 30% (but why would you do that unless you were at max Aura and at the ledge anyway :y ). Basically it's more likely to connect if lucario's damage is above something like 60% and the opponent's is above 90% (give or take depending on character fall speed and size) from what I've seen.
TL;DR -- I've personally had zero problems landing ASC JCUS since the patch so it's sitll a reliable kill setup, but ASC B-air is a lot more % specific (usually need to wait until the opponent is at or above kill % and lucario is above 60-ish%) and harder to land, but it's still doable and if within the right % range it's a kill confirm
Has Lucario always been able to reliably do down throw into a fair string? I don't remember being able to do it as well before.
I haven't tried d-air to f-air since the mobility buffs but d-throw
pre-patch had no followups unless your opponent had no idea how to air dodge :v If your opponent air dodges out of u-throw a lot a mixup you can use that can work well on fast fallers is d-throw, position yourself under them as they air dodge, and then u-smash. It's netted me some kills and victories before.
