As with other spellcasters, analyzing the tactics of the drow mage requires looking at all the different spells it can cast. But before I do that, I want to examine two other aspects of the drow mage stat block: its staff attack and its Summon Demon ability.

The staff is poisoned, of course, but it’s evidently a different kind of poison from the one used on the basic drow and drow elite warrior’s crossbow bolts. This one doesn’t impose any debilitating condition or require a saving throw; it just does a bit of damage of the poison type, like the poison on the drow elite warrior’s shortsword, only less of it. Probably, this is to compensate for the fact that the drow mage has Strength 9 (and therefore a −1 modifier to its damage) and shouldn’t be hitting people with a staff to begin with. Any drow mage who’s engaging in melee combat is either desperate or delusional.

With the Summon Demon feature, the drow mage has either a 100 percent chance to summon a quasit (CR 1) or a 50 percent chance to summon a shadow demon (CR 4). Frankly, this seems like a bizarre choice to have to make: whether or not to use an action (which the drow mage only gets to take once) that has a 50/50 chance of failing entirely. But in fact, we make this kind of choice all the time when we cast a spell that requires a saving throw to resist its effects, such as hold person. In this case, the effect is that the drow mage gets to have a shadow demon hanging around for 10 minutes. Alternatively, the drow mage can go for the sure thing with the quasit, but how badly does a CR 7 drow mage need the assistance of a CR 1 fiend?

With the power of math, we don’t have to wonder—we can calculate.

The quasit can Attack once per turn, doing 1d4 + 3 piercing damage, plus a possible 2d4 poison damage if it fails a DC 10 Constitution saving throw. DC 10 isn’t very high, so let’s say the target has a 70 percent chance of making that saving throw, for an expected 3.5 hp of poison damage on a hit. That plus the piercing damage adds up to 9 hp, and if the quasit has a 50 percent chance of hitting, we’re looking at an expected 4 hp of damage per turn. (There are also chances of imposing the poisoned and frightened conditions, but right now, we’ll just look at how much damage the little stinker can do.)

The shadow demon can also Attack once per turn; plus, it can Hide as a bonus action. Let’s assume that the average player character has passive Perception 13. The shadow demon’s Stealth is +7; this means it has a 75 percent chance to Hide successfully. The shadow demon does different damage depending on whether or not it attacks with advantage, and a hidden attacker has advantage on its attack roll. If the quasit, with +4 to hit, has a 50 percent chance of hitting, then an unhidden shadow demon, with +5 to hit, has a 55 percent chance; with advantage, this chance increases to 79.75 percent. Therefore we have two cases: a 75 percent chance that the shadow demon Hides successfully and Attacks with a 79.75 percent chance to hit for 4d6 + 3 psychic damage; and a 25 percent chance that it fails to Hide and Attacks with a 55 percent chance to hit for 2d6 + 3 psychic damage. Altogether, the expected damage per round is 12 hp.

A guaranteed 4 hp of damage per round, or a 50 percent chance of 12 hp of damage per round? According to math, we should choose the latter. Shadow demon it is!

Whew. OK. Now on to the spells.

  • Cloudkill continues the poison theme that seems to recur whenever we’re talking about drow. It’s a sustained, area-effect spell that hits the PCs’ back line the hardest, doing 5d8 poison damage on a failed Constitution saving throw and half that on a successful one every turn the PCs are in it—an expected 17 hp of damage per round each PC spends in the cloud. If you figure that the cloud engulfs four PCs (based on the estimates on page 249 of the Dungeon Master’s Guide) and that one will spend one round in the cloud, one will spend two, one will spend three, and one will spend four, this is an expected 42 hp of damage per PC altogether—assuming the cloud fills the room, so that they can’t get out of it. If the room is larger than the cloud, you have to assume that all the PCs will get out of the cloud as fast as they can, so most will take only one round’s worth of damage.
  • Evard’s black tentacles grabs PCs who flunk their Dex saves and whomps them for 3d6 bludgeoning damage each turn. With a 50 percent chance of making the initial saving throw and of breaking free each subsequent turn, this works out to an expected 10 hp of damage per target in the area of effect (I think—it’s been a long time since I worked with sums of infinite geometric series). Plus, there’s the nice bonus of restraining the PCs so that they can’t fight back. On the downside, it’s not boostable.
  • Greater invisibility is the Get out of Danger Free card. The drow mage always keeps one 4th-level spell slot in reserve for this spell, if it doesn’t cast it right away.
  • Fly is less useful underground than it is aboveground, but in a large cavern, it might allow the drow mage to engage in aerial assault, provided it isn’t concentrating on another sustained spell, such as cloudkill. Also, when transitioning from fly to greater invisibility, make sure you have a solid surface supporting you before dropping the former spell, or there may be complications.
  • Lightning bolt does 8d6 of raw damage on a failed Dexterity saving throw, half that on a success, or an expected 21 hp per target. If cast using a 4th-level spell slot, it does 9d6, for an expected 24 hp per target; using a 5th-level spell slot, it does 10d6, for an expected 26 hp per target.
  • Alter self’s Natural Weapons option doesn’t give the drow mage anything it doesn’t already get from its staff, except a 5 percentage point greater chance to hit. Thus, the drow mage will use this spell only before combat begins, as a form of disguise (consistent with its proficiency in Deception), and it will drop it as soon as combat begins so as to be able to cast other sustained spells.
  • Misty step is the only spell that grants the drow mage a bonus action. It can use this spell in combination with a damaging cantrip (see below).
  • Web does no damage but can restrain several PCs, giving the drow mage a leg up on them while they struggle to get free (which will probably take only one round, maybe two).
  • Mage armor is probably the first thing the drow mage puts on when it gets out of bed. Maybe the second thing. Assume that it’s always up and running and, accordingly, that the drow mage is down one 1st-level spell slot.
  • Magic missile does 1d4 + 1 force damage with every dart and always hits. At base level, it hurls three darts, and it hurls an additional dart for each extra spell level. Thus, it does expected damage of 10 hp cast at 1st level, 14 hp cast at 2nd level, 18 hp cast at 3rd level, 21 hp cast at 4th level and 24 hp cast at 5th level.
  • Shield is cast as a reaction. The drow mage will pop it whenever an attacker rolls between 15 and 19 to hit.
  • Witch bolt requires a ranged spell attack, and the drow mage has a good attack modifier for that (+6); it’s probably more likely to hit with this spell than with lightning bolt. However, it does only 1d12 lightning damage per round, and that’s assuming that it hits. To be assured of exceeding the damage of a single lightning bolt, the drow mage would have to sustain witch bolt for six rounds, taking no other action all the while. Of course, that’s if it casts witch bolt at 1st level. Using a 2nd-level spell slot, the drow mage can do 2d12 lightning damage per round, for expected damage of 8 hp/round; using a 3rd-level slot, 3d12 damage, or 12 hp/round; using a 4th-level slot, 16 hp/round; and using a 5th-level slot, 20 hp/round. While it doesn’t do as much damage as magic missile (and magic missile doesn’t do a lot to begin with), it does have the advantage of being a damage hose that costs only a single spell slot to turn on, giving the drow mage more staying power than the standard non-player character mage.
  • Poison spray does 2d12 poison damage on a failed Constitution saving throw—a less-than-generous 6 hp of expected damage. But hey, it’s just a cantrip.
  • Ray of frost does 2d8 cold damage on a successful ranged spell attack, for expected damage of 6 hp—and a reduction of 10 feet of movement speed. As a cantrip to pair with misty step, ray of frost beats poison spray.

Compared with the various spells the drow mage can cast, Summon Demon seems below-average, but its value lies in what it adds to the drow mage’s action economy: an independent damage-dealing agent that doesn’t consume any of the drow mage’s actions. Therefore, attempting to summon a shadow demon is always the first thing the drow mage will do. (Besides, if the summoning’s going to fail, that’s something you want to find out sooner rather than later.)

Once either the demon is summoned or the summoning has fizzled, the drow mage must decide whether or not to cast cloudkill or greater invisibility. This depends on two things: whether the room is small enough that it can trap the PCs within the poison cloud; and whether the PCs look like they can do a lot of damage, or there are more than six of them. If the drow mage casts cloudkill, it can’t cast greater invisibility at the same time, and vice versa, so it has to make the right call. One thing to note is that, unlike the NPC mage, the drow mage doesn’t have counterspell, so taking out enemy spellcasters quickly is crucial. Since they’re most likely to be in the backline, which cloudkill will hit the hardest, the drow mage casts this spell if:

  • there are at least two identifiable spellcasters in the party who aren’t dwarves;
  • the room is small enough to trap the PCs within the cloud, or at least the PCs are close enough together for the cloud to engulf at least two who are identifiable as spellcasters and not dwarves; and
  • the drow mage has an escape route that doesn’t involve moving through the cloud.

If these three conditions don’t apply, it casts greater invisibility instead.

If it does cast cloudkill, the drow mage sustains it for up to three more rounds. As long as there’s still a non-dwarf PC in the cloud, the drow mage keeps the cloudkill spell going. The drow mage always casts cloudkill at a point 20 feet away from itself—just far enough that the cloud doesn’t reach it.

Once either cloudkill or greater invisibility is in effect, the drow mage starts targeting other enemies. Again, since it has shield but not counterspell, it’s more concerned with eliminating enemy spellcasters than melee fighters. If the drow mage is invisible, it will maneuver to a position where it can line up a shot at two or more PCs, at least one of whom is a spellcaster, and fire a lightning bolt at them, using the highest available spell slot. (If the drow mage cast cloudkill, it still keeps a 4th-level slot in reserve in case it needs to cast greater invisibility later; if it cast greater invisibility, it doesn’t need to reserve the slot anymore.) Once it’s out of slots for lightning bolt, it switches to magic missile.

If it’s visible and there’s no longer a reason to maintain cloudkill, it casts Evard’s black tentacles where it can entrap the party’s melee fighters, then casts witch bolt on the toughest-looking of them, taking advantage of the PC’s restrained state to gain advantage on the ranged spell attack roll. If it’s visible, cloudkill is still in effect and there’s no melee fighter within reach, it uses the same lightning bolt tactic as described above, only after casting the spell it always completes its move to get as far from the party’s melee fighters as it can. If a melee opponent has managed to close with the drow mage, it casts misty step (bonus action) to slip out of reach, then plinks the opponent with ray of frost (action). (It uses ray of frost second, rather than first, to avoid the disadvantage that comes with making a ranged attack at point-blank distance.) If all melee fighters have escaped from Evard’s black tentacles, it tries to restrain them again with web.

Incidentally, while all this is going on, the shadow demon—which is immune to poison—is drifting through the back line, doing insensitive things to the enemy spellcasters. Once the spellcasters are down, it moves on to ranged fighters, then melee fighters.

The drow mage is fond of its skin. If it takes just moderate damage (reduced to 31 hp or fewer), it will already be thinking about retreating. If it’s seriously wounded (reduced to 18 hp or fewer), it doesn’t waste any more time thinking about it. Whether a moderately wounded drow mage skedaddles or not depends on whether it thinks its opponents can deal it another moderate wound (14 hp damage or more) in the upcoming round. If it thinks they can’t, it will keep fighting for at least one more round, dropping darkness on any enemy spellcaster still standing as long as there’s no melee attacker that it needs to misty step away from. If it thinks they can, it retreats, leaving the shadow demon behind (if one is present) as a rearguard.

Next: The drow priestess of Lolth.

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