As an addition to my previous question "How is CON save DC determined for the Behir?" there is another figure that I'm curious as to how it is determined.

If the behir takes 30 damage or more from the swallowed creature, the behir must succeed on a DC 14 Constitution saving throw... or regurgitate the creature.

Since the swallowed character is restrained and has disadvantage on attack rolls, it seems very unlikely to me that an unoptimized swallowed character in the Level 9-13 range would be able to get close to doing enough damage to cause the behir to maybe regurgitate the character. How is this damage threshold decided?

An even more challenging opponent like the Purple Worm (CR 15) also requires 30 damage to induce the CON save, while the Tarrasque (CR 30) requires 60 damage. If escaping from inside of one of these creatures is intended to be a longshot, that's fine, but I would still like to know how that damage threshold is calculated in order to keep my homebrew monster in line with existing published creatures.

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    \$\begingroup\$ I'm most interested in knowing how the damage threshold is calculated. \$\endgroup\$ Jan 7, 2020 at 15:47
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    \$\begingroup\$ Would it be sufficient to show that there is not a calculation? or at least not one that can be made consistent from observable stats of published creatures? \$\endgroup\$
    – GcL
    Jan 7, 2020 at 15:49
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    \$\begingroup\$ Yes, that is fine if there is a way to demonstrate that the damage required is decided by fiat. \$\endgroup\$ Jan 7, 2020 at 16:07
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    \$\begingroup\$ I love this question title. Just a note: since Fighters get a third attack at level 11, please consider more clearly identifying what level you are interested in. \$\endgroup\$ Jan 7, 2020 at 16:14

2 Answers 2


I am going to reverse engineer this to suggest "it's a long shot" intent

For the sake of illustration, I'll use three martial characters (partially optimized) at level 11 who get swallowed in the first round. You offered up level ranges from 9-13, so I took the middle value. When you observe that

it seems very unlikely to me that an unoptimized swallowed character in the Level 9-13 range would be able to get close to doing enough damage to cause the behir to maybe regurgitate the character.

you are correct. The analysis below shows that even with some optimization (Fighter and Barbarian cases), it is very difficult, so an unoptimized character will have more trouble.

30 HP makes it "hard to get out" for a "level appropriate encounter"

The behir case confirms your estimate that "it's supposed to be a long shot". The PC needs a little help from the dice to get that 30 HP in one round, and thus have a chance to get puked out of a behir. It is a two step process; the PC needs the benefit of slightly cold dice when the behir rolls that Con save.

Being blinded and being restrained causes attacks to be at disadvantage. This is where getting multiple blows to land can be a problem - it generally takes multiple blows (unless the paladin gets a crit on a smite) to get the 30 HP or more needed to even force the Con save. I think you can see that 30 HP is a good number to pick if the dev requires that there be a little luck involved (or maybe creative application of game features that apply advantage) to cut one's self out of a behir.


  1. Armor Class from within is 17, since that is the only AC value offered in the Behir's stat block.

  2. No magic weapons. The influence of a flat +1 or a flat +2 skews the numbers up a bit, but per some old dev comments along the lines of "the game can be completed (level 1-20) without magic items" we won't assume any.

Three martial characters seeking fulfillment as behir puke

I'll offer up three standard martial characters: A champion Fighter, a Barbarian, and a Paladin to illustrate.

Case 1: Fighter, Champion, 11, critical hit on a 19 or a 20.

Polearm Mastery, Strength: 20; Con 16, prof bonus = 4, HP = 103 (avg HP per PHB)

  • TN to hit AC 17 = 8 (17-(+5 +4) = 8) A roll of 8-20 hits

    • TN to hit, with disadvantage = 13/20 x 13/20 = .4225 chance to hit on a given attack.
    • With four attacks (three attacks and a bonus attack with the polearm mastery feat)
      ((1d10 +5 x 3) + (1d4 +5)) x .4225 = 16.4775
      That's not the 30 HP needed.
      If the Fighter took Great Weapon Fighting style (which amounts to roughly a +1 increase in DPR per attack), 19.4775, we are still not at 30 HP.
      Fighter stays in the guts without a little luck on the die rolls.
  • What about Criticals Hits? With disadvantage, we get 4 chances in 400 to score a crit: rolls of 19, 19; 19, 20; 20, 19; and 20, 20. 1.01 times the above doesn't look to improve much, but if a crit comes, great!

  • And then there's the Con save
    Let's say the Fighter rolls high and hits often enough to do 30 damage. With a Con modificer of +4, Behir needs a 10 to pass the Con save and avoid puking. On a given round, that's a 55% chance to keep the fighter in the guts and apply 21 (6d6) acid damage even if the 30 + threshold is reached.

    The Fighter took damage to be bitten {22 (3d10 + 6)} and get swallowed. On each turn after the swallow (assuming no previous damage) 21 more HP from a pool of 103. At 60 HP (at end of Behir's second turn) this fighter lasts three more rounds in the guts before the acid drops HP to 0. The total number of attack attempts from within aftger being swallowed is 4. If the Figher's are able to kill the behir before then, the fighter can crawl out.

Case 2: Barbarian, Bear Totem, level 11, Great Axe, Great Weapon Mastery

Strength: 20; Con 16, proficiency bonus = 4, HP = 115 HP. (Average)

  • Barbarian is at disadvantage, but is not subject to melee attacks inside the behir, and so Barb will use reckless attack (grants advantage) to counter the disadvantage of being Restrained.
    • Two attacks with a TN of 8. (.65 to hit for a given attack)
    • DPR is pretty straighforward, but since critical hits are speicial with GWM, we'll break this down. (Great axe is d12, average damage = 6.5).
    • 0.65 x ((6.5 +5 +3 (rage) x 2)) = 18.85.
    • Not 30 HP, unless two hits happen (37.7). Barb needs help from the dice.
      • But, with a crit, we add another 6.5 (average Great Axe damage), and another 6.5 (Brutal Critical) and another attack from GWM!
    • (.65 x 14.5) = 9.425 + 13 + 18.85 = 41.275" - well over 30 HP.
    • The chance for a crit with two attacks is a bit over 1/10. It may happen, but don't count on it.
  • Should the Barb try for a -5 hit +10 Damage GWM feature?
    • TN is now 13 so to hit is .40.
    • .4 x ((6.5 +5 +3 (rage) +10 x 2)) = 19.6. Sure, why not, it takes two hits or a crit to exceed 30 HP.
    • A single successful hit will do: 6.5(weapon) + 8(rage + Str bonus) + 10 = 24.5, better than a single successful hit doing 18.85. (Still not 30). It takes rolling a 12 on the d12 for a mighty blow to start the puking process (30 damage)
    • Two hits with the -5 / +10 will get the barfing started.
    • Barb has 8 or 9 rounds to score that kind of damage, so why not try - there is still a 55% chance to stay in the guts due to Behir's Con save.
  • The Barbarian will live longer inside the guts. Why? Rage.
    • Barb keeps taking damage, Barb keeps raging. Damage is halved.
    • Barb took damage to be bitten and get swallowed, 11 (half of 22 (3d10 + 6) piercing) damage, after the swallow and round 1 of being digested, (21 damage, reduced to 10) and has taken 21 HP from a pool of 115 ijn two rounds. At 94 HP, the Barb can last another 8 or 9 rounds while trying to cut themselves out of the Behir before the acid drops HP to 0. If the allies of the Barb are able to kill the behir before then (likely) Barb can crawl out.

Case 3: Paladin, level 11.

Str 20, Con 16, no feats, Sword and Board.
Two attacks, TN = 8, with disadvantage, to hit as Fighter: .4225.
Acid duration as with Fighter. Damage taken / HP as with fighter.

  • With one successful hit, Paladin can do, with a Long Sword + Divine Smite
    • 4.5 + 5 + 4d8 (3d level spell, smite) = 9.5 + 18 = 27.5. Almost 30 HP.
    • With two hits in one round, + smite, the Paladin is looking for puke ejection to commence.
    • With one hit, and slightly favorable damage rolls with the sword and the smite, 30 HP, start the puking.
    • With a crit, and the additional 4d8 + 1d8, 30 HP easily exceeded.
    • But, if the Behir's Con save is made some of the subsequent smite attempt roll 3d8s, 2d level spells, or 2d8's, 1st level spells, so the damage average drops a bit.

It's the Con Save that will frustrates puke ejection efforts

In any case of internal damage, there is a 55% chance that the puking won't start and the Paladin (or other swallowed character) needs help from their allies.

Your instincts are good: the numbers show that 30 HP makes it "a long shot"

It is most likely that only with the assistance of allies will the PC get out of the Behir's guts: 168 HP is what's needed to kill one with average HP.

However, a few nice rolls gives the swallowed character a chance to be puked out.

If a spell caster has Blink prepared ...

The reason why I didn't use casters in my examples are many, but spells like this is one such reason since using damage to get out is bypassed by this spell. (This spell does not require concentration).

Casting Time: 1 action Range: Self Components: V, S Duration: 1 minute
Roll a d20 at the end of each of your turns for the duration of the spell. On a roll of 11 or higher, you vanish from your current plane of existence and appear in the Ethereal Plane (the spell fails and the casting is wasted if you were already on that plane). At the start of your next turn, and when the spell ends if you are on the Ethereal Plane, you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from. If no unoccupied space is available within that range, you appear in the nearest unoccupied space (chosen at random if more than one space is equally near). {snip} While on the Ethereal Plane, you can see and hear the plane you originated from, which is cast in shades of gray, and you can’t see anything there more than 60 feet away

Out as soon as an 11 is rolled: it's not an I-win button, but it's a decent way out if the d20 isn't horribly cold. The problem a caster may have is not enough acid resistance to stay alive for more than a few rounds once that initial 22 and 21 damage (average) is taken.

In game experience with CR 1 Giant Toads and being swallowed.

Our level 11 ranger was scouting a side passage and got jumped by giant toads. CR 1. They nearly did for him when one swallowed him during round 1 of combat. He had the darnedest time getting out. Part of the problem was that he'd exit prone, and another toad would attack with advantage ...

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    \$\begingroup\$ I'm a bit confused, why are you analyzing expected damage outputs when the question is about how to calculate the damage threshold value \$\endgroup\$ Jan 7, 2020 at 18:19
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    \$\begingroup\$ @Medix2 To show how difficult it is to get to 30 HP in a single turn when attacking with disadvantage. Average damage is below 30 in each case without a little help form the dice. \$\endgroup\$ Jan 7, 2020 at 18:22
  • \$\begingroup\$ I guess I just don't quite see how this answers the question, though I may just be reading the question itself wrong \$\endgroup\$ Jan 7, 2020 at 18:24
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    \$\begingroup\$ I agree with Medix comment, but your intended answer may be a lot clearer with improved formatting of the calculations. Right now, I feel like I'm trying to dissect a 3.5 stat block. \$\endgroup\$ Jan 7, 2020 at 18:27
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    \$\begingroup\$ @Pyrotechnical is that any better? I tried to clean up the visuals. \$\endgroup\$ Jan 7, 2020 at 19:09

After considering all swallowing monsters I could find in all avaliable to me resourses, I found out two things.

1) Escape damage threshold is always a multiple of 10.

2) Creatures with higher CR have escape damage threshhold no less than creature with lower CR. No outliers here.

After fiddling with numbers I came to formula that covers all monsters from MM and VGtM (all monsters with swallow I could find):
CR×2 rounded up to next multiple of 10.

Example: Behir (CR11) escape damage threshhold = 11×2 rounded up to next multiple of 10 = 22 rounded up = 30.

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    \$\begingroup\$ There is an exception: The Juvenile Kraken must take 35 damage. \$\endgroup\$ Jan 7, 2020 at 18:56
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    \$\begingroup\$ Giant frog and giant toad don't have escape damage thresholds. \$\endgroup\$
    – GcL
    Jan 8, 2020 at 20:07

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