I'm experimenting around with MALLC using dair and uair.
Dair:
It's really hard to get a Dair MALLC with both hits using regular arts. The issue is regular arts have such a short activation period. Both hits of Dair creates such a large amount hitlag, and takes so much time that the art will likely activate before you reach the ground. It is technically possibly to do a MALLC with bot hits, but only with FH + double jump, and you must be at an exact position where you then press B and IMMEDIATELY afterwards use Dair.
However, you can MALLC with just the first hit or just the second hit.
Just the first hit: The easiest way to MALLC with Dair. Unfortunately, nothing true combos off of it. If you do it frame perfect, meaning earliest MALLC possible and using Dair at the latest time before hitting the ground, you can combo into a jab and probably a grab (combo counters don't seem to count grabs...), but that's it. They can shield before anything else. I think grab is the most useful here. Also, the opponent is sent towards whatever direction you hit them from, so a RAR beforehand makes the grab more guaranteed.
The second hit of Dair is weird to land in coordination with MALLC. Without platforms, the easiest metod is to utilize how the second hit of Dair has more horizontal range than the first hit. And that's hard. However, it is the best hitbox to use for comboing from MALLC at mid/high percents due to its low knockback angle. Dair (second hit) >> F-tilt works against rob from at least 20-70% (not finding exact percents). I only wish there was an easy way to do both hits of Dair...
Well, there is! Decisive arts
. It's easy with these. Just Full hop, shortly afterwards press B and double jump, do not fast fall, and Dair when in range. Probably plenty of other methods. MALLC Dair (both hits) >> F-smash deals 46% damage with the MALLC being into Decisive Monado Buster. Training mode. Not bad.
The other way to MALLC with the second hit of Dair is to just do a normal MALLC, but while on a platform with an opponent below you, and having the second hit poke through the platform. The timing is the same as a Fair MALLC. You can either use the soft platforms you have around on various stages, or poking through the bottom of the stage as an edgeguard. Not too sure if there are many combos from it, but it at least adds safety to your attempt.
Uair:
Uair is nice if you can land it with a MALLC. Like Dair, it's extremely hard to land both hits with MALLC unless using decisive arts. A downside Uair has to Dair is it's incredibly hard to land on short opponents. However, against those it does land on, you have some pretty useful things.
Uair (first hit) >> U-smash - any percent, kill combo. Plenty of other options.
Uair (second hit) >(jump)> FH + DJ Uair, kill combo.
Also, if the opponent is on a platform above you,
Uair (first hit) >> U-tilt works at any percent if the opponent is not to light. This could kill if MALLC'ing into Smash. Air Slash doesn't work though due to the first hitbox's pulling effect.
If they happen to air dodge, you could possibly U-Smash them.
So that's that. Hope this helps.