D&D 5E Defensive CR: determining effective hp due to resistances/immunities

[pukunui]

Hi all,

I'm a little confused about Step 9 of the custom monster stats guidelines on page 277 of the DMG. It first says "Giving a monster resistances and immunities to three or more damage types ... is like giving it extra hit points", and then says "If a monster has resistance or immunity to several damage types - especially bludgeoning, piercing, and slashing damage - and not all characters in the party possess the means to counteract that resistance or immunity, you need to take these defences into account ..."

First, do you only factor resistances and immunities into a monster's effective hit points if it has three or more?

Second, if a monster has both resistances and immunities, do you multiply its hit points for both? So like if you have a CR 6 creature that has both resistance to fire and immunity to cold and poison, would you multiply its HP by 1.5 for its fire resistance and by 2 for its immunities?

Third, what exactly constitutes "the means to counteract that resistance or immunity"? If something has immunity to cold, for instance, as long as none of the PCs can deal only cold damage, it's not really an issue, is it?

Please help!


Thanks,
Jonathan

 

[aramis erak]

I'd apply only one multiplier.

IMO:

• If it has 3+ resistances, and no immunities, use the resistance.
• If it has a total of 3+ damage types covered between immunities and resistances, with at least two from the more common 5 types (piercing, bludgeoning, slashing, fire, radiance), and one immunity in those common 5, I'd use the immunity multiplier
• if it has 3 immunities, no matter which, I'd use the immunities.

 

[Tormyr]

Hi all,

I'm a little confused about Step 9 of the custom monster stats guidelines on page 277 of the DMG. It first says "Giving a monster resistances and immunities to three or more damage types ... is like giving it extra hit points", and then says "If a monster has resistance or immunity to several damage types - especially bludgeoning, piercing, and slashing damage - and not all characters in the party possess the means to counteract that resistance or immunity, you need to take these defences into account ..."

First, do you only factor resistances and immunities into a monster's effective hit points if it has three or more?

Second, if a monster has both resistances and immunities, do you multiply its hit points for both? So like if you have a CR 6 creature that has both resistance to fire and immunity to cold and poison, would you multiply its HP by 1.5 for its fire resistance and by 2 for its immunities?

Third, what exactly constitutes "the means to counteract that resistance or immunity"? If something has immunity to cold, for instance, as long as none of the PCs can deal only cold damage, it's not really an issue, is it?

Please help!


Thanks,
Jonathan

It seems like only 1 immunity is necessary for an effective hp boost. I was calculating a MM monster, and the only way I could get the given CR was to include the poison damage immunity. As for resistances, it says several, not 3. I seem to remember calculating a monster that had 2 resistances and needing to include the effective hp modifier. It seems like only the highest multiplier is used. The means to counteract the resistance or immunity is relatively rare aside from magical weapons for piercing, slashing, and bludgeoning resistance. Elemental adept can overcome an elemental resistance or immunity if I recall correctly.

 

[pukunui]

I'd apply only one multiplier.

OK.

It seems like only 1 immunity is necessary for an effective hp boost. I was calculating a MM monster, and the only way I could get the given CR was to include the poison damage immunity.

Which monster? Not all the monsters in the MM work with the guidelines in the DMG.

As for resistances, it says several, not 3.

It does say three. Besides that, though, "several" is generally used to mean "at least three".

The means to counteract the resistance or immunity is relatively rare aside from magical weapons for piercing, slashing, and bludgeoning resistance. Elemental adept can overcome an elemental resistance or immunity if I recall correctly.

But if something has poison immunity or cold resistance, those things seem relatively easy to bypass - what character only deals poison or cold damage? It seems to me like the only ones that are really important are B/P/S.

 

[Tormyr]

OK.

Which monster? Not all the monsters in the MM work with the guidelines in the DMG.

It does say three. Besides that, though, "several" is generally used to mean "at least three".

But if something has poison immunity or cold resistance, those things seem relatively easy to bypass - what character only deals poison or cold damage? It seems to me like the only ones that are really important are B/P/S.

Gosh, I don't remember which monster, but a zombie without that boost would be a CR 1/8 instead of a CR 1/4. An Invisible Stalker would be CR 5 with just the resistances instead of CR 6 with the poison immunity.

Actually it says "several" in the "Effective Hit Points" paragraph on page 277 in Step 9. It then gives an example of 3: bludgeoning, slashing and piercing from nonmagical weapons, but it says "several." I would agree that several generally means 3 at a minimum, but with only 1 immunity being required to trigger the multiplier, I do not give the word the same weight/meaning here since it does not seem to hold true.

After searching around, I managed to find the Duergar, which only has one resistance: poison (yeah, I was looking for something else, but that is what I could find). Without the bonus from the resistance, its CR would be 1/2 instead of 1. So it looks like several means "1" for the purposes of that paragraph. It seems odd that only 1 resistance or immunity would be necessary when it says several, especially for a damage type as rare as poison.

In this case, bypassing resistance or immunity does not mean using a different damage type. It means to be able to still do full damage with the damage type. Aside from bludgeoning, piercing, and slashing from nonmagical weapons, most resistances or immunities cannot easily be bypassed.

 

[pukunui]

Actually it says "several" in the "Effective Hit Points" paragraph on page 277 in Step 9.

It says three in the paragraph above that. I quoted it in my original post. Here it is again: "Giving a monster resistances and immunities to three or more damage types ... is like giving it extra hit points"

 

[Tormyr]

It says three in the paragraph above that. I quoted it in my original post. Here it is again: "Giving a monster resistances and immunities to three or more damage types ... is like giving it extra hit points"

Ah, I missed that, sorry. Strange that they say one thing there but in practice it only requires 1.

 

[pukunui]

Ah, I missed that, sorry. Strange that they say one thing there but in practice it only requires 1.

Well, who's to say that they followed their own rules for every monster in the MM?

I just had a look at the blue dragon wyrmling (randomly). Without taking the lightning immunity into account, I get a CR of 2.5, which can be rounded up to CR 3. With it, I get CR 3 exactly, so I suppose it could go either way on that one.

But still, multiplying just once even if a creature has resistance and immunity helps. Multiplying for them separately produces some crazy results.


EDIT: Taking into account just one immunity or resistance just doesn't feel right to me, though. Take my gargantuan skeletal dragon, for instance. It has 170 hp, an AC of 17, and immunity to cold and poison. It also has Frightful Presence, which increases its effective HP by 25% to 213. If I leave it at that, it has a DCR of 10. If, however, I double its effective HP to take into account the immunities, then its DCR doubles as well to 20.


EDIT 2: Regarding the zombie, are you supposed to count a CR of less than 1 as 1 for the purposes of things like multiplying effective hit points? Otherwise, I'm not seeing how you can even figure it out, as there's no HP modifier for an expected CR of less than 1, and Undead Fortitude has no HP increase for an expected CR of less than 1 either.

I'll do the ogre zombie instead. 85 hp + 7 for Undead Fortitude = 92, which is CR 2, but it drops down to a DCR of 1/2 due to an AC of 8. The OCR is CR 2 because of its 13 damage output and its +6 attack modifier. That's a final CR of 1.25, whereas the listed CR is 2. OK, now lets include its poison immunity. 85 * 2 + 7 = 177, which is a DCR of 8, which drops down to 4 because of its AC of 8. 4 + 2 = 6 / 2 = a final CR of 3, which isn't right either. I must be either missing something in my calculations - or some of the monsters in the MM just aren't as "fine-tuned" as we'd like to think they are, going by the DMG's guidelines.

 

[Grazzt]

Well, who's to say that they followed their own rules for every monster in the MM?

They didn't. You can see that in several monsters within the MM. Follow the DMG guidelines and the CRs won't line up in some/several/a lot of places with regards to hit points, immunities, etc. But, monster design has never been a science when it came to CR. It's all about eyeballing it, comparing it to a similar monster of the same or close CR, and/or playtesting it til it "feels" right.