In D&D 5e, does falling damage max out at 20d6?
The answer to this question is “no.” Falling damage maxes at 20d6 due to the limit of six dice per an attack.
There are rare circumstances where falling can inflict more than 20d6 of damage, but they’re extremely specific and probably not what you’re looking for.
For example, imagine that a creature has just fallen off a very high place, such as the top of an impossibly tall tower. The fall is long, but this creature has a speed of 20ft . This means it falls at half speed for 10d6 damage.
Then, during the same turn it landed, the creature moves to the far end of that platform to safety. If there are no creatures waiting or standing at the end of this platform (which there likely wouldn’t be) the creature can take its turn. It moves to the end of the platform, and takes another jump back towards where it fell from. This means that in one turn, the creature can move 10ft (falling at half speed for 5d6 damage), then 30ft (a full move action).
Since this is one turn, and the creatures actions aren’t limited to one per round (it could potentially take a bonus action and attack), then this means that falling 1d6 (half speed from 10ft) plus moving an extra 30ft is equal to exactly 5d6.
In other words, there are circumstances where falling damage can be increased beyond six dice. However, these circumstances are specifically about lengthening the fall to increase damage.
