Wavejumping: Newly Discovered Move Tech for Martials?

Question

Was wondering how reasonable this ruling is RAW (RAI this was almost certainly not the intention but hey martials take what they can get). Ruling assume you're using Falling onto a Creature Rules alongside the assumption written in Xanathar's that falls are meant to be resolved immediately after ascending any amount of feet.

Wavejumping

Wavejumping is essentially a shorthop onto an opponent exploiting the fact that both jumping and falling are not things limited to once per turn, and the different triggers for when creatures become prone as a result of a fall, as described in the following rules.

Falling, Player's Handbook

At the end of a fall, a creature takes 1d6 bludgeoning damage for every 10 feet it fell, to a maximum of 20d6. The creature lands prone, unless it avoids taking damage from the fall.

Falling onto a Creature, Tasha's Cauldron of Everything (p. 170):

If a creature falls into the space of a second creature and neither of them is Tiny, the second creature must succeed on a DC 15 Dexterity saving throw or be impacted by the falling creature, and any damage resulting from the fall is divided evenly between them. The impacted creature is also knocked prone, unless it is two or more sizes larger than the falling creature.

While you land prone only if you do take damage, enemies you fall on go prone just from you impacting them on a failed save, and because falling onto a creature rules has no set height for what triggers the DC 15 dexterity save, you can jump or fly over a medium sized creature 5 ft (or 6 if you think you would just land on top of the creature by jumping 5 ft), and immediately fall into their space, giving you a chance as part of your movement to prone someone, rather than taking a action to do so.

Answer 1

Expect exploits to be patched by the DM.

This is a really interesting interaction, and I can see where you’re coming from in the strictest rules-as-written sense. However, this is an exploit, a bug, a loophole in the rules. What do I mean by this? Anything that lets you do for free what normally has a cost is an exploit. Notably, shoving another creature requires use of the attack action:

Using the Attack action, you can make a special melee attack to shove a creature, either to knock it prone or push it away from you. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them.

Attempting to knock an enemy prone normally costs your action and one of your available attacks as part of that attack action. This apparent loophole in the rules says that anyone can attempt to knock an enemy prone at least a few times per turn, without expending their action and attacks to do so. This is a textbook example of an unintentional exploit, and you can expect it to be “patched out” by the DM when you try it. I’d recommend just asking the DM before ever trying this, instead of putting them in a position to make a ruling on this in the middle of combat. And to be clear, the DM doesn’t need to come up with a rules-based rebuttal to this idea. “No, you can’t do that” is good enough.

Answer 2

So, five potential problems here:

1. The rules for falling fail to define a fall. That said, the rules for Falling from the PHB begin:

   A fall from a great height is one of the most common hazards facing an adventurer.

   And the plain English definition involves a meaningful drop. Many DMs don't count any fall of less than 10' as a fall in the first place, so you wouldn't truly be landing on someone, you'd just be trying to enter their space.

2. In order to actually fall on someone from a non-trivial height (even if you don't treat 10' as the minimum, there is some logical minimum before it counts as falling, hopping off a curb is not falling by any stretch of the imagination), you have to fall far enough to count as "a fall" before hitting them, but your total distance fallen does not subtract their height from it (arguably if you hit them, definitely if they make their save), so, for whatever you consider the minimum distance to constitute a fall, if that distance plus their height is 10' or more, you will have falling damage to split, and barring means of reducing it, you'll fall prone with them.

3. For the specific case of abusing flying movement for this purpose, the strict RAW only specify three ways for a flying creature to fall:

   If a flying creature is knocked prone, has its speed reduced to 0, or is otherwise deprived of the ability to move, the creature falls, unless it has the ability to hover or it is being held aloft by magic, such as by the fly spell.

   If you're trying to argue this ability into existence by questionable RAW claims, RAW, you can't choose to fly and then fall without one of those three things happening, and the only one you have full control over is dropping prone, which would undo the extra benefits of flying for your edge case; you could always stand up after falling, but it would consume half your movement to do so, so no making 20 attempts at this no matter what. If you're getting really technical, it's possible you can't even do that, because the rule only says you fall when knocked prone, and choosing to fall prone is not the same thing.

4. The wording "is also knocked prone" has an unclear antecedent for "also". It could be referring to the damage being split, or it could be referring to being knocked prone just like the falling character. Either way, arguably, if there is no damage to be split, or the falling character would not be knocked prone, nobody would get knocked prone.

5. Is a jump with no net change in height a fall? If not (and it's reasonable to say it isn't, because otherwise people take damage from amped up jumps), then jumping won't work to trigger this.

In practice, my personal ruling would be:

1. This can't be done with flying movement, per #3 above (which closes off the biggest exploit)
2. If you can't get at least 10' above the victim, it's not a fall, and it resolves as an attempt at a shove. Without meaningful falling speed, you can't fall on someone, they just shove you back out of their square as part of their control of the square.
3. If you can get at least 10' above the victim, you resolve the damage per Tasha's rules, and (unless you're a monk with Slow Fall or can otherwise reduce the damage dealt to you to zero), you'll end up prone at the end of it, and they might end up prone if they fail their save. If you have at least half your movement left afterwards, you can always stand up and derive some benefit from this, as they'll be prone and within 5' of you, granting you advantage on your attack(s). You'll need to be careful about how you do this, as repeated attempts, or attempts that traverse a square (cube?) within 5' of the target and subsequently leave it will allow the target at attack of opportunity.

The main remaining exploit I can see here is for monks, where they could repeatedly either spend Ki to boost their jump height if you decide a high enough jump counts as a fall even if no net change in elevation occurs by the end of it, or (at 9th level) wall-run high enough to produce a fall that would achieve the desired effect. If a DM considers this abusive, they could still rule that Slow Fall protects both faller and fallee (managing to roll with a fall while still hammering the person you fall on feels rather weird), and that a fall that deals no damage does not knock the victim prone, and that would be a reasonable reading of the rules. Or they could let you do it, because, without flying shenanigans involved, and with the likely attacks of opportunity you'll be triggering if you try to do this multiple times, it's falling within the bounds of reasonable (monks can use all the help they can get as is).

Answer 3

This could work for falling, but check with your DM

Jumping is not falling

First, jumping is a form of active movement in the game, as explained under the movement rules (p. 190 PHB)

Your movement can include jumping, climbing, and swimming. These different modes of movement can be combined with walking, or they can constitute your entire move. However you're moving, you deduct the distance of each part of your move from your speed until it is used up or until you are done moving.

Falling is passive, it does not deduct its distance from your speed, so it is separate from jumping. So jumping onto a creature is not falling onto the creature, and the rules for falling, including the optional rules for falling in Tasha's do not apply to a jumping creature.

You could potentially do this with a flying creature like an Aaracokra, by flying up, then stopping to fly and falling. However, as this answer explains in detail, technically you cannot just choose to fall as a flying creature. So a DM may well counter your tactic of a technical reading of this rule with an equally technical reading of the flying rules.

Vertical space

Vertical space is not well represented in the rules. There is no height given for the space a creature occupies. But from common logic, you can only impact a creature by falling into their space, when you fall onto them in some way, and that means that you need to be at least above the creature before you start falling.

Moreover, you cannot enter the space of a hostile creature with your movement, so you would need to fly high enough to be over them when you start falling. Depending on how tall the creature is, this may mean you need to be at a height of at least 5 feet when you start falling. As falling itself deals no damage, the benefit of repeated falling onto the same creature would be very limited. As you need to fly up at least 5 feet, and move at least 5 feet to a new space, if you have a fly speed of 50, you could at best drop 5 creatures with this tactic in one turn if they all stand next to each other and are not too tall (possibly attracting opportunity attacks made at disadvantage as you leave their reach).

Does the creature you drop on fall prone if it takes no damage?

The optional rule says:

any damage resulting from the fall is divided evenly between them. The impacted creature is also knocked prone, unless it is two or more sizes larger than the falling creature.

I think looking at the paragraph in isolation, it is most accurate to read the paragraph as you suggest: the creature you drop on has to make a saving throw, and if it fails only takes damage if there is damage from the fall to be divided. Then, new sentence, wether it took damage or not, it also falls prone, the also referring to the failed saving throw and its consequences, which do not need to involve damage.

It however also is possible to read this in a larger context: damage from the fall is shared between the creatures, and then the impacted creature is also knocked prone. That is, the also refers to not just failing on the saving throw, but it refers to failing the the saving throw and taking damage. The context here is that you yourself only fall prone from falling if you take damage, that is, there is the general idea in the game that a fall has to be substantial enough to cause damage to make someone drop prone.

I think that is a less technical reading, but one that is more in line with how the game overall handles falling, and I can easily see a DM ruling this is how they run it, so before banking on using this tactic, clear with them if they are OK with it. Also remember this is an optional rule. A DM who feels you are explointing the wording may be incentivized to shut down the rule to begin with.