Dash -> Landing Nair combos into itself at lower percents, (character dependent).
Dash -> Landing Nair also combos into F-tilt at lower percent (character dependent), Landing Nair can also combo into either CS (Cross Slash) or LB CS at certain percents.
Nair -> D-tilt is a thing as well.
Also (and most importantly IMO):
Falling Uair -> FH -> DJ -> LB Climhazzard is a possible true combo (DI dependent) and kills off the top fairly early.
In testing it earlier today with Mario on Battlefield I found it works from ~75% - 99%.
It will kill Mario from the base of Battlefield at around 95%~ (Black lightning spark appears at 95%), will kill Mario off the top platform at >= 75%~ and will kill off the middle platform at 86% (Black Lightning spark appears at 86% and above from mid platform, although can kill at 84-85%).
Will true combo before and close to kill percent, timing is fairly strict though and the hitbox of Climhazzard be a bit wonky.
Also, near kill percent typically the FH -> DJ -> Immediate Climhazzard is required for the attacks to combo and just generally reach the opponent, although before kill percent you can get away with a simple FH before Climhazzard.
This works on various characters at various percents, of course, it works on Bowser for example at 110%~, and on Fox at 86% (killing from base).
U-air can be DIed away fairly hard though so this option's utility will require further testing with DI and of course rage coming into play.
I will report back once I have gathered the relevant data for the entire cast.
EDIT: It works at even later percents when Falling Uair is substituted for FH Autocancel Dair. This may be more reliable and I will test this as well.
On a minor note Dash -> Landing Uair can allow for true combos into itself as already noted as well as into Nair or even Bair if you manage to cross up on landing.