What level should this exhaustion-causing spell be?

Question

Sap strength
Casting Time: 1 action
Range: 90 feet
Components: V, S, M (a piece of a jellyfish)
Duration: Instantaneous
Choose a creature that you can see within range. The target gains a level of exhaustion, or its level of exhaustion is increased by one.
At higher levels: You can target one additional creature.

No save!

6 castings of this spell can kill any one target, who is not immune. But it takes 6 rounds, which is longer than most encounters.
One casting is about as useful as the first level Hex. There is no concentration needed, but this does not increase DPR.

I was thinking level 2, considering you need two rounds just to halve the target's speed.
What level should this spell be?

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To avoid pulling opinion-based answers: an ideal answer will reference similar spells (if someone has homebrewed and playtested a similar effect). In the absence of that, answers from experience related to the exhaustion mechanic, effects that grant exhaustion (be it from cursed items or other penalties imposed by the DM), or other effects that impose penalties that are like exhaustion are acceptable as well.

Answer 1

This spell is not designed in a way that lines up with the 5e rules. Because this doesn't offer a save or an attack roll, I'm inclined to say that it can't be fit into the existing spell system except maybe as a ninth-level spell (many of which bend the power curve). Even if it required a save, the enormous power scaling on subsequent castings would be a problem. Consider that once they reach exhaustion level 3, the target has disadvantage on all rolls, including rolls to resist further uses of the spell.

The best evidence I have for a spell level would be fifth level. That's the level of Greater Restoration, which removes a level of exhaustion. Other effects that GR removes (Bestow Curse, Flesh to Stone, etc.) can be generated by 3rd-6th level spells, so that seems a roughly equivalent level.

However, I highly recommend a save or an attack roll, and possibly an effect of "once you successfully save against this spell, you automatically save against subsequent castings for 24 hours." Note that even the Power Word spells, some of the few offensive spells that can kill or disable without a roll, are level 8 or 9 and have HP limits that roughly correspond to the HP totals of CR ~10 monsters.

Answer 2

Frame challenge: As others have pointed out, using any spell to kill someone with no save, even if it takes six castings (which is 36 seconds, or less with multiple casters), would unbalance the game in ways that might not be resolved by increasing the level requirement.

I suggest a limitation as follows: by default, the spell increases the target's level of exhaustion by one, up to a maximum of one. At higher levels, it still increases it by one level, but to a maximum of two and then three. At that point the target has disadvantage on every single attack roll and saving throw, that can't be shaken off without Greater Restoration or a long rest. That's already pretty serious.

Comparing Hex (which only affects a single ability but adds damage); Blindness, which allows a save every turn to recover; and Power Word Stun, which is a little more severe but has a HP limit and a Con save every turn, I'd set the levels at 2, 5, and 8.

But it'd be easier to balance if you allowed a save, like almost every other debuff.

Answer 3

Before I begin... I apologize for this wall of text. This is a difficult spell, after all.

Comparing Level 1 Exhaustion with Hex

I'll start by citing a spell combo I used to do in an old campaign. I would cast either Heightened Maximilian's Earthen Grasp on a low Strength, high Int enemy; or Heightened Phantasmal Force on a low Int, high Strength enemy (usually the monsters aren't made with both stats high).

Now, both spells are notable because they are gated by a saving throw, but once you've failed, you need to make an ability check to succeed. As both MEG and PF are concentration spells, I could only hope the spell stuck long enough to be useful. The upside is, of course, the ability checks these spells require do not add proficiency.

Anyway, a party mate of mine would follow up with Hex on the target I've cast it on. This virtually prevents them from escaping the spell. On top of that, I had a save DC of 17 at level 5 (20 Cha and magic item). So even something with 20 in a stat, once they failed the first saving throw, would still find it utterly difficult to escape. And I was making sure I targeted their weaker stat for this as much as possible, stacking the dice entirely not in their favor.

The effect? We killed a Boulette with 200+ HP (it was something like 260 HP, but I'm not sure exactly) without anyone falling unconscious, and indeed, with only 1 member of the party getting attacked at all. The DM had been foreshadowing us that this was going to be a tough fight, too. And it would have been: it had 2 or 3 attacks a round, and each one did 50 damage on average! This was on top of resistances. However, the Boulette could not move due to MEG, so our ranged fighters and fighters wielding reach weapons were easily able to pick it off.

We also maimed a homebrew snake-like monster who was caught up in a PF. This one was a harder fight as it wasn't alone, but this particular creature was severely delayed (wasting ~5 rounds) and spending its action to do Investigation checks on the illusion before it broke free.

(That said, PF is much stronger than MEG, and the most utility I got from it was either outside combat or as a combat ender; as in, after I cast PF, that was also typically the end of combat)

Comparing Level 1 Exhaustion with Menacing Attack

In a different campaign, I quite enjoyed my Battle Master Fighter/Barbarian who would inflict the Frightened condition on his targets with Menacing Attack, and use a bonus action to grapple with Tavern Brawler. The Frightened condition imposes disadvantage on ability checks. This combination means I am always rolling Athletics with advantage, and the target rolls with disadvantage if they failed their saving throw. A further multiclass in Rogue gave Expertise in that skill. So, pretty much nobody was ever escaping my grip.

Many fond memories there. Grabbing pirates and throwing them overboard. Grabbing wyrmlings and holding them in place to keep them from flying away. Very memorable.

One thing I didn't get to do, though, but had been wanting to do, was team up with the party Druid and have her cast Spike Growth on me. And then I would have walked to just outside the border of that spell with a grappled opponent, but keeping them in the area of Spike Growth. With double Dash plus movement, I would have gotten 45ft in total for a round. By strict RAW, that would be 18d4 damage with no save or attack roll on the grappled creature.

Best of all, the visuals of it: prone-dragging someone's face in an area of Spike Growth feels powerful and awesome.

On Getting One Level of Exhaustion

The point I'm making from above is, disadvantage on ability checks is not something to be scoffed at. A player who takes this spell will be taking it for many reasons, and they will have many strategies up their pocket to ensure they get the most use out of that exhaustion level.

Aside from grappler builds, spellcasters will have many options like the aforementioned MEG and PF, Web, Telekinesis, Bigby's Hand, Evard's Black Tentacles, etc. These all force affected creatures to make ability checks against an effect you want to impose against them.

From my experience, targeting ability checks is a smart move. It is often not resisted, and many effects that affect attack rolls and saving throws do not affect ability checks. Even Restrained creatures, by RAW, can resist grapples with no disadvantage on the check. It follows that laying down potent effects that rely on these checks makes for some unconventional and juicy moments for the players.

Now, an effect that allows one level of exhaustion immediately gives all these strategies the green light. Unlike Hex, it requires no concentration, so a caster can lay on MEG or any of the other spells which depend on ability checks on top of that. And unlike Menacing Attack, it disallows a saving throw, so non-magical grappler builds do not even need a Battle Master maneuver and can freely multiclass into Barbarian without worrying about the concentration requirement conflicting with their Rage.

The above strategies are not bad. In fact, they can be very fun and create moments of awesome. But all this to remind you that players can be exceptionally creative, and if they take this spell, they will have a plan in place to maximize even their single cast use of it. Strategies that neither you nor I will have anticipated will undoubtedly spring from this.

Rather Accurate Secondhand Knowledge: Critical Role

Critical Role is a Twitch stream about nerdy voice actors playing Dungeons and Dragons. One thing about it is that it has run for more than 2 years now, and every session is recorded. This means, not only have the players experienced a whole slew of challenges from the DM, but the audience also sees and learns from their experiences.

For Critical Role fans: spoiler territory ahead.

In one story arc, the Frenzy path barbarian acquired a cursed sword named Craven Edge. The power of this sword was such that, on a hit, the target must make a saving throw. If it failed, its Strength score was deducted by 1 and the wielder's Strength was increased by 1. The benefits disappeared on a short or long rest.

The barbarian did not know the maximum Strength limit this sword afforded him, but he was able to use it to get to 20 Strength per battle (up from his natural 17). One day, he decided to find out.

Following a combat in which he used Frenzy (and thereby acquiring a level of exhaustion), he elected to not sleep or rest, to prevent the benefits of Craven Edge from disappearing. This earned him another level of exhaustion.

Because of his barbarian speed and Mobile feat, the halved speed was barely noticed. So, I can't provide commentary based on real games on how half speed impedes you (though it sucks to be slow).

The following day, he used Frenzied Rage once more. After the combat, he maxed out his Strength score at 25 and gained another point of exhaustion. He now had 3 total, giving him disadvantage on all his rolls.

The party then made the mistake of taking a short rest. Now the cursed item's effects come in. Due to maxing out the cursed weapon's effects in the last combat, the barbarian now has to make a Con save. He rolls a 20 and a 1. The curse? If you fail the check, you die. The barbarian died then and there.

The Lesson: Level 3 exhaustion means game over.

Now, don't get me wrong. The above scenario is probably incredibly specific. But it is an example of exhaustion killing someone without the need to get it to level 6.

When all your saves are at a disadvantage, then that is as if all spells were Heightened against you. Even Ancient Dragons or magic-resistant Liches and Rakshasas will have a hard time fending off your spells now. And with all your attacks at disadvantage, you are as good as dead in an encounter.

Now, about finding the level of the spell...

This spell is unique, which makes it difficult to place. However, we have learned several lessons from the above example:

• Imposing disadvantage on ability checks is powerful

• You only need level 3 exhaustion to kill someone

The first bullet point is there to remove any notions that blanket disadvantage to ability checks can be disregarded. At the very least, this informs us that it is at least a 2nd level spell, as it's better than Hex.

But the second bullet point is where we should truly scale this effect. The level that we want is something that will ensure that 3 castings of this spell is where the trade off happens. That is, we want to ensure that after three castings of the spell, no matter what, we've just spent enough resources to have killed someone had we cast spells other than this one, too. This applies for whether it's one person casting thrice, or three people casting once each.

Note: when I say "no matter what" above, I mean this spell should be treated as if it will always kill someone after 3 castings. This is because it has no saving throw. Other spells which require saving throws or attack rolls, which will be used for comparison, may not always kill someone after three castings.

Cone of Cold (5th level) can kill someone if they experience it thrice in a row. Each casting deals 39 damage on average, or 117 damage over three castings, but also over an AoE. But this is gated by a save, so this may actually fall to 58 damage if all saves pass, and it may become not enough.

Banishing Smite (5th level) might kill someone if they are hit thrice, and this one is gated by an attack roll. Each smite deals an average of 27.5 damage, and three hits will deal 82.5 damage.

Chain Lightning (6th level) might kill someone also. Each casting deals 45 damage on average, but it is gated by a save. This puts it on par with Cone of Cold, dealing 135 damage with three castings, but can be reduced to 67 damage if all saves are passed.

Disintegrate (6th level) might kill someone again. Each casting deals 75 damage on average, so three will deal 225 damage, but it is an all-or-nothing effect. On a save, the target suffers no damage at all.

Finger of Death (7th level) might kill someone after 3 castings. Each cast deals 64.5 damage on average, and is halved on save. This is the strongest spell so far. Three casts of this will deal 253.5, or 126.25 even if all three castings were saved.

And now we found it. Casting three Fingers of Death will always be lethal, even if they make all their saves, just like this spell. I'm stopping here because a player may not even make it to 100 HP unless they're a Fighter or Barbarian. However, if we wanted to keep going because monsters usually have higher hitpoints than 100, the only other spell that goes higher than this is Meteor Swarm.

Meteor Swarm (9th level) will absolutely kill people. Each cast deals 140 damage on average, and 70 on a save. Three castings will deal 210 damage even if all three were saved.

And so the spell level is...

In its current form, assign it between a 7th to 9th level, depending on the typical HP of your monsters. This is not there for its first casting effects, but for its 3rd casting effects. When you equate level 3 exhaustion to death, you must balance around that point because it is the peak of the spell, and not on the other times you cast it.

Final Notes

Adding a save to this spell means using it thrice will no longer "guarantee" death. This puts it within the realm of Cone of Cold and Disintegrate, which can kill someone on three failed saves, but will not do so if they pass those saves. In which case, the level can be between 5th to 6th level, but capping out at 6th level.

Obviously, this answer depends on some level of guessing as to the exact spell's level. Balancing around Level 3 exhaustion is a conservative choice. Level 4 exhaustion is effectively dealing damage equal to 50% of the creature's hitpoints that bypasses resistance and immunity -- potentially the single most devastating damage depending on the HP of the creature, and far stronger than Meteor Swarm. I'd advise you to simply not allow the spell to inflict up to level 4 exhaustion.

But if you choose to balance around this instead, then all the spell ranges potentially slide back by one (placing the spell in its current form in the 6th to 8th level range, and the spell with a saving throw in the 4th to 5th level range). This would probably be a bad idea as it means you are not equating Level 3 exhaustion with death, when a BBEG who has been imposed with such a handicap is probably going to die by the hands of the PCs rather quickly.

And remember: blanket disadvantage to all ability checks is very, very potent (remember the Spike Growth + Grapple-drag combo worth 18d4 damage per round!).

Answer 4

I want to preface this answer that only play testing will give an accurate answer, but the basis for this answer stems from comparable spells.

Specifically, I'm evaluating the Hex spell, which imposes disadvantage to ability checks tied to 1 ability score; Entangle which imposes half movement for an area; Bestow Curse which imposes disadvantage on attacks and saves; Web which restrains a creature and effectively makes their speed 0. This is of course compared to the action economy. If it takes 6 rounds to kill something that's worth something, but it's worth noting that things are really bad for the enemy upon the 3rd casting where they've been mostly nerfed into a pin cushion.

I'm going to also view this from the perspective of a PC trying to min-max things.

The first casting of the spell is really nasty and has a huge combat impact made only moreso because there's no save and thus pretty much no escape. With the exception of charisma ability checks, I can feasibly see a use for every other ability check as it relates to combat effectiveness against PCs. However, more often than not, only 2 or 3 will really matter so let's consider this similar to 3 castings of Hex, without concentration or the damage boon. This is likely to cause the target of the spell indirect damage over the course of combat, but is very subjective on how much.

The second casting halves the target's speed and consumed another spell slot. Furthermore, it's pretty much forced the target to fight to the bitter end as escape is now nigh impossible. This is likely to cause the target to suffer more indirect damage since it's ability to use the battlefield for damage mitigation purposes has been severely hampered. Getting grappled and or knocked prone is significantly more serious than previously. This effect is probably better than a 1st level spell like Entangle because the lack of a save guarantees success for the caster.

The third casting is pretty much game over for the target and consumes a third spell slot. Disadvantage on pretty much everything that matters is at least equal to 2 successful castings of Bestow Curse and this is even better because there's no save. Again, this is going to cause a lot of indirect damage as well as indirect damage mitigation.

Any further castings past this point would just be overkill. Most any encounter is firmly in hand after 3 castings against a big bad.

The DMG advises that if a spell is so good that a caster would want to use it all the time, it might be too powerful for its level.

My thoughts on this spell is that it's extremely potent. If set to too low a level, it will be used all the time. Not necessarily every fight, but every time a big bad rolls out so too will this spell. The fact that it's guaranteed to succeed coupled with increasingly damning effects which improve the party's survival versus ensuring the enemy's defeat is palpable even if it's not directly calculable.

Given that it takes 3 castings to reach something that's equal to an effect similar to a two 3rd level spells, let's start that as guidance. However, there's 2 effects at that level, so let's bump to a 4th level spell. Prior to that there's significant effects imposed by the preceding effects, the half speed with no save pushes it up at least another spell level to 5th, then you've got the effect of multiple nerfed Hexes without a save and no concentration, which I feel is extraordinarily good and warrants kicking it into the restricted spells per day category possibly around 7th level.

This might seem unreasonably high, however, consider the fact that Otto's Irresistible Dance doesn't get a save for just the first round, thereafter, saves are possible. This is worse than that. Furthermore, this causes a lot of indirect damage, if the creature can't make a Dex check to cross a narrow ridge it'll fall, if it can't make a Str check to lift a portcullis it'll be trapped in a dangerous position. With halved speed, rangers and wizards will have no trouble kiting most enemies, which is a quick death sentence; furthermore, enemies that might consider fleeing have had that option closed off from them.

The other reason I like 7th level spell is that it keeps the spell from being too good. You'd be able to cast this spell up to 4 times at 20th level, but it'd have a notable cost in what you don't cast instead. You wouldn't be using it in almost every encounter, you'd save it for something truly dangerous. Furthermore, at such a high spell level, it wouldn't be easily recoverable on a short rest the way spells below 6th are.