Hi, a bit late to the party, but during the mid percentages (20-40%), Ridley's aerials mostly all combo into each other.
reverse N-air > jab, best before 40%
Landing N-air > F-air, best around 40%
landing N-air > F-tilt-cancelled B-air / instant reverse B-air, both work just fine.
Percentages are character dependent, but work best between 25% and 40%.
Reverse landing N-air is a much easier setup for the combo (it won't require you to input an F-tilt cancel or Instant reverse B-air), but is harder to hit.
Landing U-air is hard to hit sometimes and doesn't work on any small fighters, but true combos into:
U-tilt (some MU allow for an additional U-air, but the timing is VERY strict. example: Ridley-Samus MU.)
Rising U-air.
B-air.
N-air.
F-air.
U-smash.
D-air. If timed correctly, can be a true spike and can kill very early at ledge. otherwise sends away.
majority of these combos are true into late 20s.
N-air also combos into itself starting at 0%, but gets easier into the mid 20s.
D-tilt can combo into U-tilt, but if U-tilt is turned around, a non-true B-air can be added to the end for an easy 30% combo
Neutral B combos into Dash attack, a full charge combo will result in 50% damage and works at any percent.
Ridley's B-air is also very interesting. most of these combos are exclusive to big-bodied fighters, but can work. to do most of these, Ridley must land the hitbox on his hip. B-air combos into:
itself. Best done within 25%-40% range
N-air. turn around upon landing, dash, and N-air. Best done around 30%.
F-air. turn around upon landing, and begin a rising F-air. Best done at 40%
U-tilt. Best done at 30%. I've only seen this work on Donkey Kong.
F-tilt. mid or close-range hitboxes work best. B-air can be landed in front of the opponent and work just fine. STARTS working at 11% on big-bodies, most comfortably done between 15% and 25%. (Using the hitbox on Ridley's hip will allow this combo to work into the 30% range.)
D-tilt. Mid-range hitbox can be used, hip hitbox will extend the % range. works best between 10% and 20%. using the Hip's hitbox can extend this combo's range up to 50% on certain big-bodies
Dash Attack. any hitbox can be used. combo is best between 20% and 30% for the foot or leg hitbox. the Hip hitbox can extend this combo to 50% on certain fighters.
finally, a funny mixup that's untrue but good if it lands, is D-throw > F-smash at 0%. very untrue, but can be used rarely as a mixup or easy comeback trick if the other player doesn't expect it.
none of the B-air combos