Dthrow combos into every aerial except dair (I've heard some people say dthrow > bair is a true combo depending on DI, but I've never managed it myself).
Utilt can combo into itself, nair and uair. Maybe fair as well, but I've never been able to pull it off.
Dtilt pretty much combos into everything except PKT2 if it trips. Maybe not dair, but there's no reason to use that move in that situation anyway.
Dash attack combos into uair, nair, fair and RAR bair at low percents.
FF Uair has the most combo potential. It can combo into jab, every tilt, every aerial except dair and every smash attack except fsmash. On Fox (and maybe on some other fast fallers), FF uair > utilt > nair is a true 31% combo.
Fair combos into itself (I think the max is 3 fairs in a row, 4 might be possible). It can also combo into nair and uair.
I've only managed to combo nair into itself once. Not sure how legit that combo is, but I'll lab it and come back with results.
PKT's tail can combo into PKT2. The head can combo into aerials, tilts and smash attacks if you use it to bring the other character towards the stage.
Depending on where it activates, PK Fire pretty much combos into everything if the other player is trapped in it.
Fully charged PK Flash combos into every aerial. Probably don't even need to say it, but you won't ever land this unless you happen to break a shield at 0%. Might be worth keeping in mind for style points (and a max of 52%).
These are all DI dependent and some combos won't work on floatier/lighter/shorter characters. I've got rough % guidelines on almost all of these combos. I haven't messed around with the combo potential of the weak hitboxes on aerials, but there might be some things to work with. Idk if
Yink
would want to sticky this or not.