D&D 5E Determine encounter difficulty with monsters of very different CRs

[adam_antio]

Hi guys! I don't know if there's another thread about the same topic, so sorry if there is one already.

We rebooted our campaign, and now we have a 6 men party of level 5 (I never had such such a large and powerful group before with next!). Checking the encounter difficulty table, I was astonished I had 6,600 worth of xps before any encounter would be considered mortal!

Now, I was thinking about drows, and I thought about throwing to the party a Drider (CR 6) with a bunch of standard CR 1/4 drows. However, when calculating the xp thresholds... it seems that just bringing a couple of them doubles the xp budget for the drider, and that throws everything off scale!

So what I'm asking for is: should those guidelines be treated more liberally when taking into account monsters with such a different CR? Or one lone Drider is really far less dangerous than one with two weakling drows?

 

[GX.Sigma]

The DMG says to not count creatures of a significantly lower level when determining the multiplier. This is how I interpret that:

First, determine the adjusted XP value for the encounter with the highest-level monsters. In this case, since there's only one higher-level monster, the multiplier is x1, so it's just the Drider's raw XP value.

Then, simply add the XP values of the lower-level monsters.

 

[adam_antio]

How could I miss that bit? I'm an idiot. Anyway, thanks a lot!

 

[the Jester]

I would be careful with that approach; some low level monsters can really impact a combat even if the party is higher level. Abilities like giving advantage to all attacks (via faerie fire) are very strong at all levels, so I'd go ahead and multiply, personally.

 

[FormerlyHemlock]

Now, I was thinking about drows, and I thought about throwing to the party a Drider (CR 6) with a bunch of standard CR 1/4 drows. However, when calculating the xp thresholds... it seems that just bringing a couple of them doubles the xp budget for the drider, and that throws everything off scale!

So what I'm asking for is: should those guidelines be treated more liberally when taking into account monsters with such a different CR? Or one lone Drider is really far less dangerous than one with two weakling drows?

In this specific case: yes, a drider is far more deadly with a bunch of drow along. Forget about the CR--each drow has AC 15, and you'll have disadvantage to hit it due to not being able to see it (superior darkvision means he just stays back at 115' range where he can see you but you can't see him), and every round he pops out a crossbow bolt at +4 to hit (advantage from sight/disadvantage from range cancel out) and if you don't make a DC 9 Con save you fall unconscious until someone wakes you up. Also, they're pretty much guaranteed to get a surprise round unless your party is so stealthy that the drow don't even see you (no light sources allowed). The first thing your PCs will see is crossbow bolts sprouting from their chests. If the PCs close to melee range, one or two drow can cast Faerie Fire while others engage in melee or continue to pump crossbow bolts from close-range.

I don't know how many drow you were thinking about using, but 7 drow and a drider meet your Deadly threshold, so I'll assume that. And yes, 7 drow and a drider is an encounter that's actually worthy of the Deadly label. As in, non-zero chance of TPK. I don't know the details of your party, could be 5% chance of TPK, maybe less or more--but the drow are definitely making the drider tougher.

Honestly, the encounter would be scarier without the drider. Same XP value of drow alone = 33 drow for a Deadly encounter. Sure, they're a tiny bit more vulnerable to AoE spells, but against AC 18 PCs they'll be doing 63 points of damage per round from 120' range, and forcing 11 Con checks to stay conscious! The wizard with a Fireball isn't going to be getting off very many Fireballs under those conditions. A drider isn't worth 27 drow in a fight. It's worth maybe 4 drow tops.

 

[adam_antio]

Ok, so when building encounter with vastly different CRs, I should not factor the lowest ones in the multiplication if and only if they really don't bring something significant at the table. I was planning 5 drows, so with a couple of faerie fires and three of them shooting from the dark, the drider becomes very a very lethal brute. Well... that's a difficulty of 5.100 xps... I think I totally like that for a difficult encounter!

Thank everyone for you're valuable input!

 

[DaveDash]

Here is what I do:

(CRx * multiplier) + (CRy * multiplier) + (CRz * multiplier)

Level 16 campaign now, and the current multiplier system is really starting to show its flaws. Anything 5 CR's below the main monster shouldn't generally increase the multiplier by double, just because there are three creatures total. EG 1*CR14 + 2*CR8's against my group really wouldn't be twice as difficult as 1*CR14.

I just ran a combat that against my level 16 group that was CR12 + CR8 * 3 + CR7 * 4 + CR4 and it felt "Medium" instead of "Deadly", in terms of both encounter difficulty level and resource consumption.

The other thing to consider as well is that not all CR's are created equal. Certain monsters in combination with certain other monsters are way more powerful. The guidelines are useful in the beginning when you're new, but don't become to shackled to them. I've started just throwing them out entirely now and doing it based on feel rather than math.

I'm running an underdark campaign, I've used Drow in large numbers, across a wide range of CR's, and they get burnt to a crisp pretty quickly (well, more like Hold Person'd to death). My players have also laughed off the faery fire saving throw, with things like Bless + Paladin Aura.

 

[Celtavian]

I tend to use the guidelines in the DMG to start. Then I take into account terrain and the special abilities of each creature running loose mock combats to see how the battle would turn out using the tactics I intend to use for the monster. In the case of the drow, do the PCs have easy access to light capable of countering their darkvision? Are the drow in an area they can use their superior darkvision to their advantage? If the PCs can provide enough light to figh the drow on equal ground or the area doesn't allow the drow to use their superior darkvision to their advantage, then I don't think the encounter is too deadly. If the drow can use their darkvision to their advantage and deny light to the PCs, you might have a very deadly encounter. I'd run a few mock combats on your own just to see how a few rounds of combat go.

 

[FormerlyHemlock]

There's another benefit to running mock combats: you learn the stats by heart, and you also get your rules mistakes and tactical mistakes out of the way. Things like forgetting to have the drow cast Faerie Fire, or forgetting what the range is on Faerie Fire, or granting the drow advantage for being in the dark but forgetting to apply disadvantage because hand crossbows have short range, or getting the DC wrong on their sleep poison, or having the drow forget to retreat 30' after firing (thus making it too easy for PCs to close) or not using cover where it's available, etc.

I actually spent all this evening writing myself a little simulator which throws 2 PCs and their minions up against giant ants using semi-optimal tactics... it's not as good practice as running the battles manually, but it gives me a feel for how tough the PCs actually are. (To my surprise, they can actually handle 5x as many giant ants as I expected without TPK... the monk survives.)

 

[DaveDash]

+1 for running mock combats.