Deadly Falls (5e Variant Rule)
From D&D Wiki
Fall damage in 5e is very simple: for every 10 feet you fell, you take 1d6 bludgeoning damage, to a maximum of 20d6. It's easy to remember and it works... for the most part. It works until the 8th-level warlock falls 80 feet and doesn't even lose half their hit points, a fall that would easily kill most creatures in the game, especially us. This variant rule seeks to fix this with some simple changes.
First, the limit is limit on damage changes from a number of d6 to a number of feet fallen. Simply increasing the maximum number of d6 doesn't do the potential damage justice, so with this rule a character stops accumulating fall damage once they've fallen 200 feet. Second, the damage accumulates at an increasing rate. We start with 1d6 damage for every 10 feet fallen, but for every additional 10 feet fallen you increase the added damage by another 1d6. This means that if you fall 20 feet, the first 10 feet deals 1d6 damage while the last 10 feet deal an additional 2d6, totaling for 3d6 bludgeoning damage after falling 20 feet. A 30-foot fall works in the same way: the first 10 feet adds 1d6 damage to the total, the next 10 feet add 2d6, and the third 10 feet add 3d6, for a total of 6d6 bludgeoning damage after just a 30-foot fall. This nearly-exponential increase in damage continues in this fashion almost indefinitely. A 40-foot fall would deal 10d6 damage, 50 feet would deal 15d6, 60 would deal 21d6, and so on, all the way to 210d6 after falling from a height of 200 feet.
In addition, creatures of different sizes are affected by falling differently. Tiny creatures are considered to have fallen only 10 feet for every 20 feet they fall. Small , Medium, and large creatures experience falling as normal. Huge creatures subtract 10 feet from their total fall distance, meaning they would need to fall 20 feet to experience any damage, or 210 feet to experience the full 210d6. Finally, Gargantuan creatures subtract 20 feet from their total fall distance but are considered to have fallen 20 feet for every 10 feet they fell beyond those first 20, meaning after falling just 30 feet they would take 3d6 damage, and after 50 feet they would take 21d6 damage.
The aim of this ruleset is to help prevent your players from yeeting themselves off cliffs without a care in the world and expecting to live to tell the tale. I do not care that your character is 18th level: jumping off that 200-foot cliff should disintegrate your bones, liquify your organs, and turn your skin into a nice rug. However, the other changes help prevent stupid little pitfalls from murdering creatures that shouldn't even care about the comparatively miniscule drop in elevation, like a giant accidentally breaking its ankle just because it jumped into a 15-foot pit. Not that the base game's 1d6 bludgeoning damage would really affect the giant's hit points that much, but the number of times 1 or 2 hit points made a difference in my combats is truly astounding, and that fall damage could be the reason why the giant doesn't get the last turn in combat to kill that dying PC. The reason why Gargantuan creatures accumulate falling damage so much faster than smaller creatures is because of their sheer mass and how it affects their maximum velocity: short distances are still nothing to them, but beyond that it really makes a difference just how far they fell. Keep in mind, though, that the distance cap still exists: a gargantuan creature will be considered to have fallen 200 feet once they've reached 120 feet, and any distance fallen beyond that won't add to the damage. Despite these changes, the best part about this is that a 20th-level barbarian can still survive this damage, provided they are raging and they get lucky with the damage rolled being just slightly below average.
I first got the idea for this change when I had the exact situation mentioned at the beginning of this variant happen to me: a freaking *warlock* jumped off an 80-foot cliff just to enter combat, and they still had half their hit points left. The character didn't even have a high Constitution score! So, I decided that the fall damage rules were stupid and made my own. Honestly, situations where you have to deal with falling don't come up very often in the course of an average combat encounter, but just in case you want your characters to fear the roc carrying them up high just to drop them to their doom, then this is the change for you!