Help calculating CR/statistics for a custom monster

[Platypusbill]

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I'm preparing an encounter for a 3rd-level party of three adventurers (a Half-Elf Swashbuckler Rogue, Half-Orc Open Hand Monk, and a Human Shadow Sorcerer). The encounter will involve a scarecrow (CR1) and a witch, basically a Devil's Tongue Tiefling with 6 levels of Fiend Warlock. The preliminary iteration of the witch is built almost entirely as a PC, except it has an extra Eldritch Invocation and the Dark Devotion trait from Cultists, but no Pact Boon. Stat block:



The intention is that the encounter is deadly and the characters will probably need to spend most of their resources to overcome it, as they are fully rested and this is pretty much all I expect them to run into before their next long rest. To that end, a CR 1 (the Scarecrow) and a CR ~3 monster should challenge them appropriately according to the DMG guidelines.

As of now, the monster building rules say the witch has a defensive CR of 1/2 and an offensive CR of 2, for an average of 1. However, there are many variables that are going to affect the difficulty of the fight, which makes this difficult to balance:

-The scarecrow might be able to get a surprise round and/or Unseen Attacker advantage because of False Appearance. I am going to roll perception checks, which might let the characters notice it before this happens.

-The scarecrow's Terrifying Glare is going to be pretty devastating if it lands (slightly less than 50/50 chance on average) because the paralysis eats the target's actions for one round, grants advantage to the next attack of the scarecrow and the witch, and melee attacks auto-crit. The witch's Vampiric Touch then has a roughly 80% chance of hitting and a 50% chance of knocking out the paralysed PC (except the Half-Orc Monk) instantly, on top of healing the witch for half as much. Vampiric Touch is likely to be the go-to action for the Witch as it's pretty powerful in this scenario, and the ability to use it multiple times as long as the concentration is held helps compensate for having only two spell slots.

-The Sorcerer may end up wasting resources and a turn to cast Darkness, which she can see through (she managed to more or less trivialise a previous encounter with this) only to find that the witch (but not the scarecrow) can also see through it.

-Armour of Agathys could also be pretty powerful because it grants 15 THP and deals 15 damage with no save to melee attackers (both the Rogue and Monk are mainly melee fighters) and it's likely to require two hits before it is depleted. Might allow an Arcana check to recoginse the spell so they know that they can use ranged attacks to deal with it.

Overall, do you think these factors are enough to consider the witch a CR 3 monster? She is pretty squishy for CR3, especially if she doesn't spend a turn to cast Mage Armour, but I feel the spells and other abilities could cause the fight to spiral out of control. Of course, DM fiat can be invoked to adjust things as the fight progresses if it's too hard (e.g. poor target selection, such as using the Terrifying Glarge + Vampiric Touch combo on the Half-Orc Monk) or too easy (e.g. she could get the Pact of the Chain familiar and use an action to summon an imp).

[Unoriginal]

The average of 0.5 and 2 is 1.25, rounded down to 1.

My advice is to not "DM fiat" things to make them harder or easier. Just play the monsters as smart as they're supposed to be and see how the encounter goes.

Now, your monster could very well be a challenge for the group, but I'd advise to give them a +1 to their spell save DC/bonus to hit with spells.

[Ninja_Prawn]

The average of 0.5 and 2 is 1.25, rounded down to 1.

I've heard that you're actually supposed to 'average' offensive and defensive CRs by moving up or down rows in the table, rather than computing arithmetic mean. That is to say that the average of 0.5 and 2 is exactly 1, with no rounding needed.

But I agree that it's not worth it to try to modify CRs post-hoc to account for environmental factors and inter-monster synergies. The system is intentionally vague and fuzzy and CR was never meant to be a precise measurement. Just roll with it an see what happens.

Also, spell selection should be accounted for in the monster's CR already, so you shouldn't be worrying about that.

It's like... a kobold's CR doesn't change just because it's being led by Tucker. The encounter is more difficult, of course, but that doesn't change the essential nature of the kobold. To put it more philosophically, the kobolds are part of the encounter, but the encounter is not part of the kobolds. Does that make sense?

[Talamare]

I would do CR2

She has a lot of powerful spells

[Unoriginal]

I've heard that you're actually supposed to 'average' offensive and defensive CRs by moving up or down rows in the table, rather than computing arithmetic mean.

That's true for the calculation of the Offensive CR and Defensive CR, but then you have to do the normal mathematical average of those two values.

But I agree that it's not worth it to try to modify CRs post-hoc to account for environmental factors and inter-monster synergies. The system is intentionally vague and fuzzy and CR was never meant to be a precise measurement. Just roll with it an see what happens.

Also, spell selection should be accounted for in the monster's CR already, so you shouldn't be worrying about that.

It's like... a kobold's CR doesn't change just because it's being led by Tucker. The encounter is more difficult, of course, but that doesn't change the essential nature of the kobold. To put it more philosophically, the kobolds are part of the encounter, but the encounter is not part of the kobolds. Does that make sense?

True.

[UrielAwakened]

Caveat: The CR system is terrible. It only cares about 4 things really: How much HP you have, how much AC you have, how much your primary attack/casting attribute is (accuracy) and how much damage you do in your first three rounds. It cares a little bit for traits and things but not really.

From the eye test this isn't a CR 3 monster. It has 45 hit points and nothing for AC. It's going to get rofflestomped by a party of level 3 adventurers. It's probably a CR 1 monster.

[Unoriginal]

Caveat: The CR system is terrible. It only cares about 4 things really: How much HP you have, how much AC you have, how much your primary attack/casting attribute is (accuracy) and how much damage you do in your first three rounds. It cares a little bit for traits and things but not really.

The CR cares about the the relevant traits, saves and the like, and of course a combat-efficiency measurement is going to care about AC/HP/to-hit bonus/damages more than the rest. Nothing terrible about that.

From the eye test this isn't a CR 3 monster. It has 45 hit points and nothing for AC. It's going to get rofflestomped by a party of level 3 adventurers. It's probably a CR 1 monster.

Well yes, you're right. As pointed out earlier, OP miscalculated the CR.

However, it should be pointed out that OP didn't take into account the Armor of Agathys (and I'm not sure the Mage Armor was included either).

[Platypusbill]

The average of 0.5 and 2 is 1.25, rounded down to 1.

Derp. Back to elementary school I guess.

The CR cares about the the relevant traits, saves and the like, and of course a combat-efficiency measurement is going to care about AC/HP/to-hit bonus/damages more than the rest. Nothing terrible about that.

However, it should be pointed out that OP didn't take into account the Armor of Agathys (and I'm not sure the Mage Armor was included either).

IIRC the HP pool gave it a defensive CR of 1/4 and the AC from Mage Armour bumped it to CR 1/2. It does require an action to apply, but it could also be pre-cast if the witch is being paranoid.

The thing is, between the THP from Armour of Agathys and the Fiend feature and the healing from Vampiric Touch, there is going to be a lot more HP to chew through.

[UrielAwakened]

The CR cares about the the relevant traits, saves and the like, and of course a combat-efficiency measurement is going to care about AC/HP/to-hit bonus/damages more than the rest. Nothing terrible about that.

No, it's terrible. Anything that's a save-or-die or a save-or-suck doesn't factor into it at all.

A monster with 45 hit points, 13 AC, and Wish is the same CR as one without it by their incredibly flimsy and overly complicated monster creation rules.

[gloryblaze]

No, it's terrible. Anything that's a save-or-die or a save-or-suck doesn't factor into it at all.

A monster with 45 hit points, 13 AC, and Wish is the same CR as one without it by their incredibly flimsy and overly complicated monster creation rules.

Unless the base monster can do 7d6 damage in a 60 foot cone every turn, I imagine Wish -> Illusory Dragon would increase the offensive CR quite a bit. Wish -> Abi-Dalzim's Horrid Wilting for a 12d8 aoe on turn 1 might help as well, but probably not as much.

[Unoriginal]

No, it's terrible. Anything that's a save-or-die or a save-or-suck doesn't factor into it at all.

Actually, it does. The Save DC is included in the CR calculation.

A monster with 45 hit points, 13 AC, and Wish is the same CR as one without it by their incredibly flimsy and overly complicated monster creation rules.

Transparently wrong. Giving that creature Wish would make its damage output equal to the one of any lvl 8 spell.

[UrielAwakened]

Actually, it does. The Save DC is included in the CR calculation.



Transparently wrong. Giving that creature Wish would make its damage output equal to the one of any lvl 8 spell.

The save DC is only included in terms of the accuracy dimension. And it's only used as a modifier once the damage for the first three rounds is calculated. Doesn't sound like you understand how the math works.

If you have zero damage-dealing spells, it doesn't matter what the DC is. It still has no effect on the final CR. If the monster is going to use Wish to cast spells that do zero damage, then it adds nothing to its CR. In this case you would just use the damage it deals with its physical attacks over three rounds and modify that with its attack modifier. If you don't like the Wish example since it has versatility, pick literally any other spell that doesn't deal damage and it's the same thing. Give a CR 1 monster banishment and it's still a CR 1 monster.

It's a bad system.

[Unoriginal]

It might shock you, but most spells that don't deal damage lack the ability to directly deal with PCs. Which is what CR is about.

Sure, a monster can do things like postponing a fight with Banishment or Wall spells, or trick PCs into dangerous situation with illusions, but that's not what CR is about.

Effects such as a Medusa's gaze attacks are special cases. I admit including those special cases in the rules could have been beneficial, but they probably didn't want to spend much space explaining an exception.

As for not understanding how the math works...

For the quick calculation:

If the monster relies more on effects with saving throws than on attacks, use the monster's save DC instead of its attack bonus.

For the longer method:

The save DCs to resist such effects have a direct bearing on the monster's challenge rating, and vice versa.

Try to understand the rules first, before doubting others.

[UrielAwakened]

So what you completely missed, again, is that attack bonus is ONLY used as a modifier on damage. You never, ever, ever just use the spell DC as its offensive CR. The spell DC ONLY modifies the damage DC.

If the monster has zero damage-dealing spells, you don't use its spell DC ever in the calculation. You use its attack bonus and damage from basic attacks. If I have to seriously spell this out for you:

Defensive CR:

1) Calculate HP CR
2) Adjust up or down based on its AC.

Offensive CR:

1) Calculate damage CR (use the average damage over three rounds, keep in mind how many targets it can hit with area of effect spells).
2) Adjust up or down based on its attack modifier (or DC if it primarily deals damage with spells) (except not really because proficiency bonus is going to matter too so really these charts are garbage unless you know what CR you want it to be already).

And again, there are spells that legitimately kill PCs or make monsters impossible to deal with at a certain CR, and they have no weight whatsoever in a CR calculation. The monster creation rules cannot account for such monsters. I know how this works, I built a monster maker in excel using VBA and then abandoned it once I realized how awful WotC's monster creation rules actually are.

They are bad rules devoid of nuance.