NPC Damage Tables

I put myself in a situation this week. My group’s doing a dungeon crawl, a mean one involving talking weapons and super tetanus, which means there’s a drought of social interaction. So I did this thing which you too may have read as a suggestion to spice things up: I added an NPC group of adventurers. And I introduced them through combat versus a shared enemy.

Cue an hour of me frantically rotating between stat blocks, rolling attacks against myself, roleplaying with myself, and trying to keep track of all this plus the shenanigans of my players. It was very masturbatory, but not in a good way.

In this case I did it to myself (even though, as I said, this is definitely a thing that people say you should do). But official modules will happily throw you to the dogs as well: Out of the Abyss starts with no less than ten NPCs (CRs ¼, 2, ½, 1, ½, ¼, ¼, 0, 2, 2) and Tomb of Annihilation drops a nine NPC free-for-all in a 30×30 room when you break a mirror of life trapping (CRs 0, 6, 3, 5, 7, 3, 10, 9, ⅛). The latter comes with a brief script that is guaranteed to be irrelevant after one turn of player intervention.

Full Sim vs Full Narrative

There are two extremes you can take. You can play all these NPCs straight; roll their attacks as normal, look up ACs and defensive measures of their targets, keep track of hit points, etc. That is definitely the fairest way to handle things in terms of the game systems, and there is something to be said for fairness. You need fairness to back you up when you kill your players’ characters, and you need to kill your players’ characters to keep combats tense.

The other extreme is full DM fiat. You narrate how all the NPCs are punching each other and when it feels good to you, you remove some of them from combat. If a monster’s hit points become relevant, you make it up. This is the easiest and smoothest way to handle it, and you need those to prevent your game from stalling and losing momentum.

Average Damage as a Sweet Spot

I like to lean towards the narrative side, adding systems only when required; add just enough rules to hang my hat on. And really all you need for is to answer “how much damage does this monster deal to its enemies per round”.

From the DMG’s creating a monster section:

Note how attack bonus and armor class pretty much cancel each other out across the board. That means a monster generally has a 50% chance to hit another monster of a similar CR rating.

That changes when a monster hits one of a different CR, but only marginally so. Searching for a case where the hit rate is halved to 25% or “doubled” (actually: the miss rate halves) to 75%, you’ll need a CR 2 monster fighting a CR 17, or a CR 8 fighting a CR 3. That’s the difference between an assassin killing a veteran in 4 rounds or 3.

So, just have monsters deal half their average damage per round. Thanks to the linear progression of the DMG’s monster damage table, this damage can be calculated with a simple formula: damage = CR * 3 + 3. For low CR monsters, the damage is simply 1, 2, and 4, although in practice those deal more damage at the cost of fewer hit points so I’d just cap damage at 4.

The +3 in that formula is inelegant, but remains relevant for surprisingly long (it starts accounting for less than 10% of the damage at CR 10). Personally, I opt for simplicity and err on the side of lethality, particularly since using this damage, monsters take 6-9 rounds to kill each other, so I’d just multiply the CR by 4 instead.

The NPC-on-NPC Combat Rule: Each round, a monster deals damage to another monster equal to its CR (rounded up) times 4.

Trying it out

The mirror of life-stealing shatters and pours out a host of creatures: a commoner (4 hp, CR 0), an invisible stalker (104 hp, CR 6), a minotaur (76 hp, CR 3), a troll (84 hp, CR 5), a drow mage (45 hp, CR 7), a doppelganger (52 hp, CR 3), a four-armed gargoyle (147 hp, CR 10), a champion (143 hp, CR 9) and a stirge (2 hp, CR ⅛).

According to the book, most of the monsters attack or help the party, or flee. The ones that fight each other are:

• The champion and minotaur attack the gargoyle, destroying it in 4 rounds, and then help the characters deal with the invisible stalker and the troll.
• The stirge attacks the commoner, killing him in 1 round. After draining his blood, the stirge flies away to digest its meal.

If we play this out:

Round 1

• The champion and minotaur deal 9*4 + 3*4 = 48 damage to the gargoyle (99 hp left).
• The gargoyle hits the minotaur for 40 damage (36 hp left).
• The stirge deals 4 damage to the commoner, killing it, and flies away.

Round 2

• The champion and minotaur deal another 48 damage to the gargoyle (51 hp left).
• The gargoyle slays the minotaur.

Round 3

• The champion hacks the gargoyle for 36 damage (15 hp left).
• The gargoyle deals 40 damage to the champion (103 hp left).

Round 4

• The champion finishes off the gargoyle.

Alternate History

It looks like the system generates a similar result to the one described by the book! Plus now I can go off-script. What if the drow and the doppelganger duke it out while the invisible stalker joins its gargoyle buddy in fighting the champion and minotaur?

Round 1

• The drow mage deals 28 damage to the doppelganger (24 hp left).
• The doppelganger slams the drow for 12 damage (33 hp left).
• The champion and minotaur deal a 48 combined damage to the gargoyle (99 hp left).
• The gargoyle hits the minotaur for 40 damage (36 hp left).
• The invisible stalker hits the champion for 24 damage (119 hp left).
• The stirge kills the commoner.

Round 2

• The drow mage kills the doppelganger (24 hp left).
• The champion and minotaur deal another 48 damage to the gargoyle (51 hp left).
• The gargoyle slays the minotaur.
• The stalker hits the champion for 24 damage (95 hp left).

Round 3

• The drow would rather take his chances with the humans than the invisible monsters and statues, so starts blasting the gargoyle, for 28 damage (23 hp left).
• The champion finishes it off.
• The stalker hits the champion once more, dealing 24 damage (71 hp left).

Round 4

• The drow hits the stalker for 28 damage (76 hp left).
• The champion joins in and adds 36 damage (40 hp left).
• The stalker assaults the champion for a further 24 damage (47 hp left).

Round 5

• The drow and champion finish off the stalker.

Round 6

• The champion sticks out her hand to thank the drow, who performs his sudden but inevitable betrayal, dealing 28 damage (19 hp left).
• The champion, enraged, slashes the duplicitous drow for 36 damage, killing him! Nice try, drow mage!

Alternate Round 7

• Or you could say that the drow surprised the champion, giving him an extra round wherein he deals another 28 damage, vaporizing the poor champion!

TL;DR

So yeah, a lot of text to say “try having NPCs deal 4 times their CR damage when they’re fighting each other”.

Ok, bye!