Figuring out tactics for spellcasters is always complicated by the need to assess the relative merits of their spells, which requires application of game-theory math along with examination of their action economy. I’ll start with the mage non-player character, basically a level 9 wizard.

Before looking at spells, let’s look at abilities. Strength is below average, Dexterity above average: a mage is a ranged attacker by preference. Intelligence is very high: a mage knows which enemies to target with which spells. Wisdom is above average: a mage prioritizes self-preservation. In fact, given the amount of training and education a wizard has to undergo in order to do what he or she does, and also given how squishy magic-users typically are, I’d say the mage has an above-average interest in self-preservation and will commence escape protocols after taking only moderate damage (reduced to 28 hp or fewer).

There’s no reason for mages to employ weapons except in the direst of circumstances. They’ve got +5 to hit with a finesse weapon attack (that includes the dagger that the NPC mage is armed with) vs. +6 to hit with a spell attack, and even the fire bolt cantrip does 2d10 damage (11 hp on average) vs. the dagger’s paltry 1d4 + 2 (4.5 hp on average).

Mages have only one spell that can be cast with a bonus action: misty step. That simplifies their action economy but also limits what they’re able to do in a single turn. Since a spellcaster can cast no more than one leveled spell in a combat turn, misty step is likely to be combined with the fire bolt cantrip as a matter of course. Shield and counterspell are cast as reactions, enabling mages to buy time but also imposing a need to conserve their spell slots for these spells.

It looks like mages have a lot of spell slots (14 altogether!), but this is deceptive. Shield and counterspell can suck away two of those slots per round, not to mention the slot a mage uses on his or her own action. A mage has to finish a fight fast. And with a 17 Intelligence, he or she knows it. Consequently, the mage’s strategy looks something like this:

  • Always have a way to escape.
    • Position yourself where you can get to an exit, using misty step to maneuver if needed.
    • If the room you’re in has only one exit, draw your attackers away from that exit so that you can use it yourself.
    • If the room you’re in has a window, always keep it open so that you can use fly to get away.
    • Decamp before you run out of spell slots.
  • Avoid taking damage.
    • Suppress opponents’ actions.
    • Stay more than 30 feet away from opponents, using misty step to maneuver if needed.
    • Use shield and counterspell to thwart incoming attacks.
    • If possible, cast mage armor before combat begins.
  • Do the greatest damage to the most enemies with each spell.
    • Cast area-effect spells and multiple-target spells before single-target spells.
    • Cast spells that impose debilitating effects on top of damage before damage-only spells.

Greater invisibility is a beaut: it takes care of both escape and damage avoidance. In fact, it can potentially obviate the need to do any damage at all. But a mage who wants to fight—out of either enmity toward the player characters, the need to defend a location or item, or a generally antisocial personality—may keep this spell in pocket, focusing first on dealing damage.

Mage armor, conveniently, lasts 8 hours with each casting. A particularly paranoid mage, or one who lives a life of danger and knows it, might keep mage armor up all the time. This means always being down one 1st-level spell slot, possibly two, further increasing the need to finish fights as quickly as possible. A less paranoid mage might toss mage armor up only when he or she hears a suspicious noise, an alarm is triggered or a messenger runs in with a warning. Mage armor is an indispensable spell, but inconveniently, it’s also one that may not be worth the action it takes to cast if combat is already under way. A mage who’s caught off guard will need to prioritize damaging and disabling his or her opponents over adding those three points to his or her armor class, which will only reduce the chances of taking damage, not negate them.

As I noted in my discussion of the mummy lord, the value of a spell slot has less to do with its level and more to do with its scarcity. The mage’s 5th-level spell slot is extra-special, because there’s only one of it. The mage will use this slot only to cast cone of cold; he or she will never waste it on boosting a lower-level spell. All the mage’s other spell slots, however, are effectively interchangeable, except to the extent that certain spells require certain slots to cast.

With that in mind, let’s look at what each damaging spell can do:

  • Cone of cold does 8d8 cold damage on a failed Constitution save, half on a success, affecting creatures in a 60-foot cone, or approximately six creatures (see conversion estimates on page 249 of the Dungeon Master’s Guide). If we assume a roughly 50/50 chance of making this saving throw (which I will throughout this analysis), this does expected damage of 27 hp per creature to six creatures, for a total expected damage of 162 hp.
  • Ice storm does 2d8 bludgeoning damage plus 4d6 cold damage on a failed Dexterity save, half on a success, affecting creatures in a 20-foot-radius cylinder, or approximately four creatures. Thus, it does expected damage of 17 hp per creature, a total expected damage of 69 hp. It also turns the storm’s area of effect into difficult terrain, slowing enemies from approaching or pursuing the mage.
  • Fireball, everyone’s favorite, does 8d6 fire damage on a failed Dexterity save, half on a success, affecting creatures in a 20-foot-radius sphere, or approximately four creatures. Thus, it does expected damage of 21 hp per creature, a total expected damage of 84 hp. Cast with a 4th-level spell slot, it does 9d6 fire damage, expected damage of 23 hp per creature, total expected damage of 95 hp.
  • 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, 17 hp cast at 3rd level and 21 hp cast at 4th level.
  • Fire bolt does 2d10 damage to a single target and requires a successful ranged spell attack roll to hit; I’ll rate this as about a 70 percent chance to hit. Thus, it does an expected 7 hp damage. Stop the presses! (Then again, it’s a cantrip. It’s a bit of free damage you get to do when you cast misty step. To complain is churlish.)

Sorted preferentially by damage done (and nothing else), we have cone of cold, fireball (4th level), fireball (3rd level), ice storm, then a big drop-off in damage when we get to magic missile cast at any level. In fact, magic missile’s damage when cast using a 3rd- or 4th-level spell slot is so poor compared with fireball and ice storm, we have to conclude that the mage never casts magic missile at these levels, ever, and probably doesn’t bother with the spell at all unless he or she is facing fewer than four opponents and is merely trying to finish them off—or is entirely out of 3rd-, 4th- and 5th-level spell slots, at which point it’s long past time to skedaddle.

We’re starting to get a picture of the mage’s spell priorities, but we’re not fully there yet, because there’s a logjam at spell level 4. This is the slot the mage needs in order to cast greater invisibility, but it’s also the slot needed for ice storm, and we’ve already seen that a 4th-level fireball does even more damage than ice storm, but ice storm impedes movement in a way that fireball doesn’t. I’d say that because of its utility in both escaping and avoiding damage, the mage always reserves one 4th-level spell slot for greater invisibility even if he or she doesn’t cast it first thing. Fireball at 4th level is the mage’s first go-to for damage, but he or she doesn’t use that last 4th-level spell slot until it’s apparent whether he or she will need to cast ice storm to impede the PCs’ movement or not—for instance, if they show a propensity toward charging at the mage. If it’s clearly unnecessary, that last 4th-level slot can be spent on another boosted fireball; if the necessity becomes clear, ice storm. In the meantime, the mage can cast fireball using a 3rd-level spell slot instead, which still does more damage than ice storm.

But wait—there’s also a logjam at spell level 3! This is the slot the mage needs in order to cast counterspell or fly. The former is indispensable. The latter is indispensable if and only if the mage has a window to fly out of. If there’s no path of airborne escape available, that frees up a 3rd-level spell slot for another counterspell or fireball. Are you starting to see why it’s so essential that the mage end this fight as quickly as possible? Two rounds, maybe three, then bail out: that’s the most the mage will allow.

Round by round, then, here’s the mage’s combat heuristic:

Round 1

  • Do the PCs look like they can do a lot of damage, or are there more than six of them? Cast greater invisibility (action) right off the bat.
  • Do the PCs look like a nuisance more than a threat? Cast cone of cold (action).
  • Has an attacker just rolled a 12 through 16 on an attack roll (15 through 19 with mage armor up)? Cast shield (reaction) to repel it. (This applies on every subsequent round as well.)
  • Has an attacker just cast a spell of 3rd level or lower that can damage you or keep you from getting away? Cast counterspell (reaction) to negate it. (This applies on every subsequent round as well.)

Round 2

  • Did you cast greater invisibility in round 1? Cast cone of cold (action) now.
  • Are you visible, did any enemy close to melee distance, and can you see a place where you’ll be more than 30 feet from any enemy? Cast misty step (action) to get there, then fire bolt (reaction) against any attacker who’s damaged you so far. (This applies on every subsequent round as well.)
  • Are you visible, did any enemy close to melee distance, and can you see no place where you’ll be more than 30 feet from any enemy? Cast greater invisibility (action) now.
  • Are you visible, and do you have no enemy within melee distance? Cast fireball (action) now, using a 4th-level spell slot.

Round 3

  • Are you visible and moderately wounded or worse? Cast greater invisibility (action) and get out of there. (This applies on every subsequent round as well.)
  • Are you visible, do you have no enemy within melee distance, and do you have a reason to keep fighting? Cast ice storm (action) if the PCs have been trying to get within melee distance; otherwise, cast fireball (action) using a 3rd-level spell slot, unless you need to keep one open for fly, in which case go ahead and cast ice storm after all.
  • Are you invisible, and do you have a reason to keep fighting? Cast the best damaging spell you have available to you, and keep moving around to maintain a decent distance from any enemies.

Round 4

  • Do you have only one or two opponents left, and will they be easy to pick off? Magic missile (action), 2nd-level spell slot.
  • Are your remaining opponents clustered? Cast fireball (action) using a 3rd-level spell slot, unless you need to keep one open for fly; in that case, cast ice storm.
  • Look, this is already starting to go on too long. Cast greater invisibility (action) if you’re still visible or cast fly (action) if you have an open window, grab the nearest thing of value (free action), and get out of there.

Round 5

  • What are you waiting for? Get out of there.

Well, that was fun, wasn’t it? Two thousand words already, and I haven’t even gotten to the archmage yet! I’ll save that NPC for my next article.

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