Allright, so I tested the true combos from a cancelled Dair.
Remember that the ones that pop the enemy in the air can be tetched, so they turn into tech-chases.
Here are the guaranteed follow-ups, all of them are tested on Mario in training mode, with the rage always nullified by eating an heart container, and with no DI, also, the range in wich the percentage will work, is before the Dair connects. Also, the attack are pergormed as soon as possible, some of them might true combo if delayed, but then the reward would be overshadowed by the one of slower and stronger moves:
Jab
Is true between 5% and 23%
It deals 27%
FThrow
Is true between 5% and 18%
It deals 32%
How do I know that it is true if the combo count resets when I grab? Because the grab has the same start-up of his jab.
Dthrow->Wizard Dropkick
Is true between 17% and 18%. Yes, it is literally a single percent window, at least against Mario, but remember that this window is needed for the DThrow to combo from the calcelled Dair, the DThrow->WDK alone is true until 49%.
It deals 35%
DTilt
Is true between 8% and 17%
It deals 32%, however, the DTilt has more range than the grab so you can connect it more easily.
FTilt
Is true between 10% and 19%
Deals 32%
DSmash
Is true between 17% and 23%
Deals 40% if both hits connect, 25% if only the first one does
USmash
Is true between 27% and 36%
Deals 43%
It requires precise spacing, you may need to hypen smash or reverse the USmash depending on wich part of the Dair hits.
I tested togheter short-hopped aerials and full hopped ones, though that shouldn't matter that much given the knockback scaling of the Dair.
Nair
Is true between 17% and 62%
Deals 31% as only the first hit connects, 28% if the second does. Deedless to say, if you do everything correctly, you will always hit with the first hit.
Also, technically the Nair has the same start-up as the jab, however, because of the new buffering system, you can't short hop and Nair as fast.
Uair
Is true between 15% and 73%
Deals 32%
Having a wider reach where this combo is possible and dealing more damage, this combo is always better than the Nair, unless Stale Move Negation comes in play.
GANNON-BAN COMBO 1
I want to continue on the path of "Hell Drop" and call this
Phantom Crusher
Fair
It's true between 30% and 67%, at starting from 50% at the ledge, even without rage, the combo throws Mario to the blast line, just the perfect situation to complete a GANNON-BAN.
Note that in order for it to be a true combo, you must hit with the hitbox above Ganon's head
GANNON-BAN COMBO 2
Death hand
Bair
It's true between 20% and 59% and is a GANNON-BAN combo for the same reason as the Fair, with the difference that from the ledge and without rage, it needs 40% in order to throw Mario to the limit of the blast line.
The two following GANNON-BAN combos aren't guaranteed, but unlike the previous two, they cause the death of Mario no matter what, in other words, they aren't guaranteed to connect but are guaranteed to K.O. Mario, so you can use them as mix-up between the true combos, since they are just too powerful to ignore. Speaking of this, the third needs 30%, to hit properly an unprepared opponent, the 4 needs 40%, both need both you and your opponent at the ledge, and cause the death of Mario no matter what, guess some of you already understood at what I'm referring to.
GANNON-BAN COMBO 3
Shadow crush
You can jump over Mario and deathspike him with the wizkick, Ganon will land onstage
GANNON-BAN COMBO 4
Abyss choke
Aerudo
Guess you know what to do next
TL;DR: DAIR IS BROKEN.
I discarded the rest of the moves either because they didn't have any true combo(FSmash) or because they weren't neither fast or stong enough(both in damage and knockback) to have some uses in combos(Dark Dive and Wizard Dropkick).
The only one that might have some use is Dark Fists, but I still havent't it.
On a side note, i find it fairly easy to cancel the Dair by short-hopping, and Dairing on reaction when I see Ganon that starts falling down.