I confess that this blog is substantially shaped by my own biases. I’m not a fan of underground dungeon crawls, so I tend to give less attention to monsters that are found only, or predominantly, in the Underdark. Also, I find it more interesting to write about monsters whose features interact in complex ways, meaning I’m more likely to gloss over simple brute fighters.
For both these reasons, I haven’t touched the duergar yet. Their ability scores follow an unambiguous brute profile, their Duergar Resilience and Sunlight Sensitivity features are passive, and they’re armed with ordinary melee and ranged weapons. Generally speaking, their “tactics” are going to consist of charging, bashing and stabbing.
But a reader recently wrote, “I can never figure out when to Enlarge and when to turn invisible, especially when using them in groups.” These two specific questions are worth examining. Unfortunately, the former, in particular, demands math.
Enlarge increases the duergar’s size, Strength (not numerically, but in the form of advantage on ability checks and saving throws only, not attacks) and damage, at the cost of one round’s action. Except in the case of grappling, damage is the only one of these benefits that really counts. Since time is so valuable in fifth-edition Dungeons and Dragons, we have to calculate whether this benefit is worth the cost.
Let’s start with raw damage numbers—assuming hits for the sake of simplicity, because the probability of a successful attack is the same regardless of what weapon the duergar is using or what its current size is. Let’s also assume that the duergar is using its higher-damage weapon, the war pick. (You can do the math with the javelin; the conclusion will be the same.)
A hit with a normal-size duergar’s war pick does 1d8 + 2 damage, or 6.5 points on average, which I won’t round because the half-points are going to accumulate over time. An Enlarged duergar hits for 2d8 + 2 damage, or 11 points of damage on average.
Here’s how it breaks down over the length of a typical combat encounter (using the “round-to-even” method for accumulated damage):
D&D 5E assumes that the average combat encounter lasts three rounds, with two to five being typical. Here we see that three rounds is the approximate break-even point, at which Enlarge offers only a slim benefit. If a battle is going to drag on more than three rounds, the benefit of Enlarge is substantial. If it’s going to be over quickly, Enlarge works to the duergar’s detriment.
But how do we know how long a battle is going to last? We don’t—and neither does the duergar. We can only make educated guesses based on what we know about encounter building, and the duergar can only use intuition shaped by experience.
Let’s consider the possibilities:
- An Easy encounter will be over quickly and decisively in the player characters’ favor.
- A Medium encounter will last two to four rounds, with only light to moderate damage to the PCs.
- A Hard encounter will last three to five rounds, and the PCs may take moderate to serious damage.
- A Deadly encounter may last three to five rounds, with the PCs taking serious to deadly damage—or the PCs may get clobbered quickly. We’re going to have to distinguish between “Deadly” and “Super-deadly.”
In an Easy encounter, the duergar gets no benefit from Enlarging—and also has no hope of winning. Our reader wanted to know when to use Invisibility? Well, here you go. A duergar has only average Wisdom, but that’s enough for it to know when it’s badly outmatched and ought to flee.
A Medium encounter is harder to judge, but there’s still only about a 50/50 chance that Enlarging will be of any significant help to the duergar. In this instance, it may recognize its predicament immediately, use Invisibility and flee; otherwise, it will use Enlarge, then realize its mistake, use Invisibility and flee.
A Hard or Deadly (not Super-Deadly) encounter, however, is likely to drag on, and in this case, the benefit of Enlarge is indisputable. The duergar will use this feature in the first round of this encounter—earlier, if it can, but don’t cheat and throw already Enlarged duergar at your PCs if the duergar would have no reason to expect a fight. The duergar will only turn invisible and flee if and when it’s seriously wounded (reduced to 10 hp or fewer).
A Super-Deadly encounter is likely to be over relatively quickly, and the duergar is favored to win it. In this instance, it doesn’t need to flee, and it doesn’t need any greater advantage than it’s already got. So it will fight at its normal size.
I’ve been referring to singular duergar here, but the same rules apply if they’re attacking (or defending) in the plural. Use the Encounter Building rules on pages 82–84 of the Dungeon Master’s Guide to determine each encounter’s difficulty and the reaction of your duergar to it, which may differ from encounter to encounter.
But wait, you may be asking, doesn’t the difficulty of fighting a duergar differ depending on whether it’s fighting normal-size or Enlarged? Won’t that affect the challenge rating, and therefore the difficulty of the encounter?
Not really. The reason is, the duergar only fights at normal size when it’s got an overwhelming advantage. Otherwise, if it’s going to stick around and fight, it does so while Enlarged, and its CR assumes Enlarged damage. (It also seems to count Duergar Resilience as full Magic Resistance for the sake of calculating defensive CR—at least, that’s the only explanation I can come up with for its having CR 1 rather than CR 1/2.)
Anyway, the long and the short of this is, you don’t have to think about duergar tactics on the fly. All you have to do is figure out the difficulty of each duergar encounter beforehand, so that you know how the duergar will react to the PCs: vanish and run, Enlarge and charge, or simply charge.
Next: catoblepas. Catoblepases? Catoblepates?