Simic Hybrid's Manta Glide (GGR p. 20) states the following:
You have ray-like fins that you can use as wings to slow your fall or allow you to glide. When you fall and aren't incapacitated, you can subtract up to 100 feet from the fall when calculating falling damage, and you can move up to 2 feet horizontally for every 1 foot you descend.
When you fall, do you subtract up to 100 feet from the fall distance or the fall damage calculation afterwards (10d6 falling damage)? Both are part of the calculation of fall damage so which step does it apply to?
The first interpretation means that this trait will not have any effect on a fall that is greater than 300 feet because falling damage caps at 200 feet (20d6) whereas the second interpretation will always allow you to subtract 10d6 falling damage from a fall of any height.