D&D 5e: Houserule: Falling, Jumping, & Collisions

OK, so a few people have pointed out some really wonky aspects of the fall damage rules in the PHB. I am among the people who agree that the fall damage rule is not functional in representing what it was intended for. So I rewrote it.

First off, the original rule gave no fall rate. As such, it is not possible for a flying character to go into a dive and then resume flying to gain movement distance on the vertical plane. Furthermore, it seems to be assumed that the moment a creature begins to fall, it instantly hits the ground, regardless of how high up they were. This means it is also impossible for a player to try and catch a falling character without an improvisational DEX check outside of initiative order. Xanethar's Guide to Everything finally gave us a fall rate, but it is a little incorrect. They give it as 500ft per 6 second turn. The actual terminal velocity of the average human body is 1,038ft in 6 seconds. For my rule, I rounded this down to an even 1,000ft per turn.

The next problem, and the more commonly cited one, is that there is a damage cap on fall damage. The rule is 1d6 bludgeoning per 10ft fall distance up to a limit of 20d6. The problem is that it is not unusual for player characters to reach HP scores in the hundreds. 20d6 deals an average result of 70 damage. It effectively means that once characters of certain classes reach a certain level, they can confidently jump off an airship at 20,000ft and suffer only a heavy blow. Now, I did some theory crafting, and it looks like the maximum HP possible without magic using only the core rules is about 450. For a fall to be an almost guaranteed kill on a maxed out character, you need 150d6 to produce an average result in that range. But you know what's even more effective? Having no damage cap. It's just 1d6 per 10ft. All the way. That way, no matter how much HP a character has, high altitude drops are always a guaranteed kill, even if they're overkill.

The next point isn't mentioned as much, but fall damage is based on the idea that the falling thing is human-like. It makes no consideration for monster size/mass or object properties. I can fix this. The damage die is determined by the creature/object size class, while the count of the die is determined by the distance fallen. Smaller objects have less mass so they need to fall greater distances for that mass to cause more damage. Large objects have more mass, which means they take more damage from less distance fallen.

The next problem is that there is no rule for collisions. What kind of damage happens if you drop one enemy on another enemy? To handle this, I created a simple collisions rule. To prevent people from abusing this rule to engage in physics engine combat to deal extra damage outside of the standard action economy, I added an exception that disallows players from intentionally causing a collision without taking an action to do so.

My collisions rule also has a provision for lateral collisions due to causes other than fall damage. This rule, being general, is replaced by any specific rule that mentions collisions caused by it. This rule exists primarily for figuring out what happens when vehicles ram into each other, and to determine damage dealt by thrown objects that lack the thrown property.

Finally, there's some awkwardness I've found regarding how objects and creatures travel through the air via jumping, which has some interaction with falling and collisions. Specifically, how far does one need to drop before it is considered falling? I can jump down from a 10ft drop and be fine, and I'm not even in halfway decent shape. How far could a violence-loving athletic hero go before they tear ligaments absorbing the landing? I created a rule to hanle this by adding a drop distance calculation to the jump rules.

Finally, the jump rules don't scale for non-medium creature. The consequence being that riding horses aren't very impressive at leaping obstacles the way they should be. Likewise, other big agile creatures like giant and dragons are restricted to relatively small hops. To fix this, I added a rule that modifies all of the jump distances, (long jump, high jump, and drop limit) based on size class. This also makes it so that the Tarrasque doesn't take fall damage by stepping down a few stories from a ledge.

THE FALLING RULE:

When a creature or object begins to fall, they fall at a rate of 1,000ft per 6 second turn, or 10,000ft per minute turn. If a creature or object collides with the ground while falling, it takes 1 damage die of bludgeoning damage per 10ft fallen. For falls from great heights, fall damage is measured cumulatively across turns in which a character falls continuously. The fall damage die is determined by the creature or object's size class, following this chart:

Tiny d4
Small d6
Medium d8
Large d10
Huge d12
Gargantuan d20

THE COLLISIONS RULE:

When a creature or object collides with another creature or object due to a fall or from being thrown, it is possible that the objects will take damage from the impact. This damage is equal to the fall damage the instigating object would have taken on impact with the ground. If the collision is not happening in free fall, the damage is halved. If the two objects were thrown toward one another and collide simultaneously, they take double damage. If a character intentionally attempts to cause a collision, they must use their action to make an attack on the target of the collision, using their dexterity modifier if they are using an object to cause a collision, or their strength modifier if they themselves are the projectile. Otherwise, objects are assumed to pass targets by unaffected, colliding only with structural features of the environment like walls and floors.

For example, a player throws a chair, (Medium object) at another character 25ft away. (I would be using my throwing range rule to determine whether this is even possible, but it likely is.) They make a dexterity ranged attack check to throw the object at their target. On a hit, the target and chair take 2d8/2 bludgeoning damage from the collision.

THE JUMP RULES EXPANSION

A chreature can drop from one level to another without taking fall damage as long as the distance is within their strength score in feet.

For example, a character with 18 strength can drop 18 ft without it being considered a fall.

Additionally, a character can take half damage from a fall up to double their strength score by making a dexterity saving throw against the total distance fallen. Whether they succeed or fail on this save, they land prone.

For example, if a character with 18 strength falls 20 ft, they can take half fall damage on a DC 20 dexterity save.

Falls of a distance exceeding double your strength score deal full fall damage on impact.

Drops and falls do not consume your movement speed.

The long jump, high jump, and drop distances are based on the assumption that the creature in question is medium in size and humanoid in form. For creatures of other sizes, adjust those ranges by the percentage given:

Tiny 25%
Small 50%
Medium 100%
Large 150%
Huge 200%
Gargantuan 300%

For example, a riding horse has a strength of 16. If it were medium, its long jump distance would be 16ft. Because it is large, its jump distance is increased by 8ft to a total of 24ft, 150% of the base value. This is consistent with reality as the longest recorded jump distance for a horse was 28ft.
Another example, the tarrasque has a total drop distance of 30ft, which is 300% of the 10 feet the base rule would apply. This means a tarrasque could stand on top of a 3 storey building and then jump down from the side of it to street level without taking any damage whatsoever.
As a final example, an ancient black dragon could do a running high jump 90 feet vertically into the air, (27+3*3) before spreading its wings to take flight. It could also fly within 81ft of the ground and simply fold its wings to dive at the ground without taking any damage whatsoever or spending movement speed to do so.