D&D 5E Calculating NPC CRs

[Archade]

So, I'm looking to convert my favorite AD&D module, Against the Cult of the Cult of the Reptile God, and I'm trying to figure out NPC CRs.

To create Snigrot Dogroot, a 3rd level Rogue (Assassin), what sort of CR modifiers should class abilities like sneak attack, cunning action, assassinate, or a poisoned dagger have? The DMG is silent on the matter ...

 

[Tormyr]

The DMG says to use the biggest, baddest, most efficient damage dealing that your monster can do for 3 rounds and average them.

Sneak Attack: If Snigrot will be attacking with an ally, figure this into the damage calculation every round. Otherwise, calculate it in only the first round (from stealth/surprise).
Cunning Action: Does not affect HP, AC, DPR, AB or Save DC, so it does not affect CR.
Assassinate: If it is likely that Snigrot will be able to surprise someone, calculate the additional damage into the first round only.
Poisoned Dagger: Figure it into every round.

So if Snigrot did 1d6 piercing plus 1d6 poison per round and gets an extra 1d6 from sneak attack and has a dex mod of 3, it would look like this:

Round 1: 24 damage. Assassinate deals automatic critical hit. 2d6 +3 piercing +2d6 sneak attack and 2d6 poison.
Round 2: 13 damage. 1d6 +3 piercing, 1d6 sneak, 1d6 poison
Round 3: 13 damage. 1d6 +3 piercing, 1d6 sneak, 1d6 poison

Average is 50 / 3 = 16. So 16 would be the effective DPR used in the CR calculation. That puts Snigrot in the Offensive CR 2 category, but his attack bonus is 5 instead of the expected 3, so his Offensive CR is increased to 3. Then you just need a Defensive CR of 3 to have an average CR of 3 at the end. If he has studded leather (which is AC 12 + dex I think), that would make his AC 15. If you give him about 91 hp, that would put him in CR 2 territory, and the AC 15 being 2 higher than the expected AC of 13 would bump him to a Defensive CR of 3.

So HP 91
AC 15
DPR 16
AB 5

gives you a CR3 Snigrot Dogroot. Of course, there are several things that could be added that would modify the effective HP, AC, DPR, and AB, but it is a start.

 

[Archade]

So, let me see if I have this right ...

Snigrot is posing as an unarmored cook, with an AC of 12, and 18 hit points. He's not technically that dangerous.

Let's say for argument's sake that Relentless Endurance adds +1 to effective AC, and Cunning Action (comparing to the similar goblin ability) grants +2 to effective AC, that would set the defensive CR at 1/4.

Offensively, he has a dagger poisoned with serpent venom, It would do 1d4+2 normally (4.5), putting him at CR 1/4. Sneak +2d6 attack adds +7 damage on the first round, and serpent venom adds +3d6 damage, or +10 for the first three rounds. Assassinate creates an automatic critical on a successful surprise attack, so call it another 2 points of damage on the first round. That means damage would be 24, 15, and 15 damage, or 18 points average damage, butting his offensive CR at 2. Having a +5 to hit moves it to CR 3.

If I average the two, it should bring the final result to CR 2. Does that sound correct?

 

[Leatherhead]

Offensively, he has a dagger poisoned with serpent venom, It would do 1d4+2 normally (4.5), putting him at CR 1/4. Sneak +2d6 attack adds +7 damage on the first round, and serpent venom adds +3d6 damage, or +10 for the first three rounds. Assassinate creates an automatic critical on a successful surprise attack, so call it another 2 points of damage on the first round.

Crits roll all damage dice again, including the Sneak attack +2d6

So 2d4+4d6+3d6(or 6d6 if your venom allows for no save) +2 for the first round attack. So 32~ or 42 damage on the first round.

 

[Tormyr]

So, let me see if I have this right ...

Snigrot is posing as an unarmored cook, with an AC of 12, and 18 hit points. He's not technically that dangerous.

Let's say for argument's sake that Relentless Endurance adds +1 to effective AC, and Cunning Action (comparing to the similar goblin ability) grants +2 to effective AC, that would set the defensive CR at 1/4.

Offensively, he has a dagger poisoned with serpent venom, It would do 1d4+2 normally (4.5), putting him at CR 1/4. Sneak +2d6 attack adds +7 damage on the first round, and serpent venom adds +3d6 damage, or +10 for the first three rounds. Assassinate creates an automatic critical on a successful surprise attack, so call it another 2 points of damage on the first round. That means damage would be 24, 15, and 15 damage, or 18 points average damage, butting his offensive CR at 2. Having a +5 to hit moves it to CR 3.

If I average the two, it should bring the final result to CR 2. Does that sound correct?

Okay, with those stats
HP 18 plus 7 effective hp from Relentless starts him at DCR 1/8.
Natural AC of 12 plus 4 effective hp from Nimble escape bumps that up to 1/4.

The most effective attacks that would normally come up are used. If there is another person to fight with, then sneak attack will always happen. Assassinate does a critical on a successful hit, so that doubles all dice. So the first round should be 42 (2d4 dagger + 2 + 4d6 sneak + 6d6 poison). Second and third round would be 21.

Average DPR is 28 for an OCR of 4.
4 attack bonus gets an effective boost of 4 from nimble escape. This boosts OCR by 1 for a total of 5.

The average CR is 2.625 which rounds to 3. However, this guy could kill a 3rd level PC outright with his average first round damage.

 

[Tormyr]

Having looked at Snigrot, he seems like someone who shouldn't even be getting into combat. His poisons are ingested, not added to a weapon. I would suggest not worrying about his stats and focus on him trying to poison the PCs. If for some reason you do need a stat block, I would suggest using the CR 1 spy on page 349 of the Monster Manual.

 

[Archade]

I'm taking the time to convert the 4-5 npcs from the adventure, rathher than use npc stat blocks. That being said, the cultist npc is going to get a lot of use.

Snigrot in the module has a +1 dagger ... I was trying to tone that down (along with a bunch of the other treasure), with a poisoned dagger instead. I may have to rethink that for CR calculation, if nothing else.

So far, the module seems right, with CR 1-3 encounters, except for the CR 8 spirit naga. I guess I have to look at Ramne and see what sort of difference he might make ...

 

[Tormyr]

I'm taking the time to convert the 4-5 npcs from the adventure, rathher than use npc stat blocks. That being said, the cultist npc is going to get a lot of use.

Snigrot in the module has a +1 dagger ... I was trying to tone that down (along with a bunch of the other treasure), with a poisoned dagger instead. I may have to rethink that for CR calculation, if nothing else.

So far, the module seems right, with CR 1-3 encounters, except for the CR 8 spirit naga. I guess I have to look at Ramne and see what sort of difference he might make ...

The poisoned dagger is much more deadly than the +1 dagger. The +1 dagger only gives a 5% better chance to hit and only adds 1 damage. So you get 5 damage done on that 1 extra hit and 1 damage overall vs. 1d6-3d6 (whatever you choose) on each hit. CR favors the poison.

I would suggest keeping the +1 dagger. Daggers are hardly ever used. This might be an interesting opportunity to see if someone chooses something "suboptimal".

 

[koga305]

Cunning Action: Does not affect HP, AC, DPR, AB or Save DC, so it does not affect CR.

You actually did a great job of summarizing the process but I disagree with this assessment. If you look at the Goblin's Nimble Escape (which is actually less powerful than Cunning Action because it doesn't allow Dash) in the Monster Features table on page 280-281, you see that it adds 4 to the monster's effective AC and attack bonus assuming the monster hides every round (presumably this is from Advantage). If that's the tactic you see Snigrot taking, then I'd go ahead and use this modifier, and also factor in Sneak Attack every round. If he's not hiding every round, then maybe you could lower the bonus.

 

[Tormyr]

You actually did a great job of summarizing the process but I disagree with this assessment. If you look at the Goblin's Nimble Escape (which is actually less powerful than Cunning Action because it doesn't allow Dash) in the Monster Features table on page 280-281, you see that it adds 4 to the monster's effective AC and attack bonus assuming the monster hides every round (presumably this is from Advantage). If that's the tactic you see Snigrot taking, then I'd go ahead and use this modifier, and also factor in Sneak Attack every round. If he's not hiding every round, then maybe you could lower the bonus.

Yeah, you are right. Cunning action should have the same bonus as nimble escape. However, in this particular case, Snigroot is stuck in the kitchen with nowhere to go, so it would not help him there.