This article was first broadcast in Episode Sixty on 6th February2019.
Killer DM: Oh dear. Why is my favorite organ donor lying on the floor? If he’s dead and I didn’t kill him I will be very upset.
ROSTRO: Inquiry. This situation has been explained previously. What is the source of confusion?
Killer DM: Oooooh you’re all big and flashy. Are you that new thing Ryu’s been worried about?
ROSTRO: Creature personality profile re-analyzed. Greetings. I am the Realized Oikumenatal Solution To Removing Obfuscation. You may refer to me as ROSTRO. I assist Ostron with more complex issues of a mathematical nature.
Killer DM: I thought Ryu said we’re talking about how to create deadly encounters for high level characters. Surely Ostron doesn’t need help with that.
ROSTRO: It is possible he received a post-hypnotic suggestion that mathematical analyses in the future should involve me regardless of complexity.
Killer DM: Oh we’re going to get along just fine.
The official D&D resources have a large number of monsters or potential creatures available to create an opposing force for the players. Mountains can easily be filled with giants, dragon lairs can have kobold guardians clogging the caverns, and swamps can belch forth hags, trolls, crocodiles, and giant spiders to hinder adventurer’s progress.
But let’s say you’re running a campaign that doesn’t have the players crawling through the wilderness. Say they’re somewhere like Waterdeep and they just watched their only high charisma, level-headed bard decide that stabbing the local crime boss in front of his boys is the way it’s going to be, and now everyone’s fighting in the streets. Along come the city watch to restore order!
Well I hope they emptied a few watch posts because they’re going to need at least 10 of the boys in blue before the players will start to worry about their chances, at least based on how difficult the Challenge Rating numbers say the encounter will be. Sure there will be consequences down the line in the story, blah, blah, blah but sometimes you want to be able to put a clearly fatal encounter in front of the players without having to explain why fifteen demons from the pit are suddenly showing up in the middle of a sylvan glade.
The root of the problem reveals itself through examination of the aggregate monster list. Few creatures above CR 13 are medium size and even fewer are humanoid. Further, above CR 10 the few humanoid and medium sized creatures listed primarily rely on spellcasting. Assembling a challenging collection of creatures that are at once medium-sized, terrestrial in nature, and non-magical is difficult.
Scenario: a collection of 13th-level characters press aggressive action against an anti-magic cult made up of humans. The DM desires this combat persist for multiple rounds. Human NPC statistics do not facilitate this. Resolution: Select an alternate creature, spread disinformation.
For further theoretical analysis, posit a group of level 10 characters attempting infiltration of a stronghold guarded by elite soldiers.
Even if you use the Veteran stat blocks, which are CR 3, you have to get them fighting quite a few of them before anyone starts worrying. Also having 8+ elite soldiers every time will probably make the heroes question how elite the soldiers really are; I mean, if five murder-hobos are mowing through the army’s elite in one night how hard can this war be to win? Or rather, how bad is the other side that they’re worried about this?
Now on the other hand, up at CR 6 you have a Hobgoblin Warlord. No magic, mundane weapons and armor, medium sized, and no abilities that are really outlandish. Throw just three of those beauties at the players and they should be really questioning how long until they need to start drawing up new character sheets. Now, you could work in a subplot about hobgoblin mercenaries or something, but in my opinion it’s much, much easier to just tell them these are badass humans that are better than you. My word is law, you shall not question it.
Unfortunately simply describing an aesthetic difference for creatures is not commonly feasible. The need for such a creature usually presents itself when a so-called “boss” class foe is required. However, even if you are able to find reasonably sized, non-spellcasting examples, there are many creatures that derive their higher CR from abilities beyond the realm of most mundane beings.
Let’s say you need a dangerous mercenary around CR of 14. On the surface an Ice Devil may appear to be a good candidate to simply claim they are another type of being. They’re large size, but you can fudge that down to medium without upsetting balance too much. Where you run into problems is looking at the creature’s other abilities. It has damage immunities and resistances all over the place, and its attacks add ice damage. Difficult to believe all of that would be coming from a random human in charge of some mercenaries.
Fortunately the DM’s guide provides a whole section on how to modify creatures to make sure the players have no hope of survival.
Now, this gets mathsy really fast so my whirring, beeping friend over here is taking over soon but even for those of you who need calculators just to total dice rolls there are some handy tables in the book. On page 274 there’s the table that tells you how to figure out a creature’s CR, and you can tell after a little bit of study that it’s based on a combination of AC, Hit points, attack bonus, and damage per round. Start jacking up those statistics on a creature and it’s CR goes up right along with them.
But my favorite cheat sheet is on page 280. It takes a lot of the various abilities creatures get and tells you how to translate them into a mundane improvement to the creature. Is the creature resistant to magic? Just get rid of that and bump up its AC by 2 instead. Does it have a charge attack? Just add the charging damage to one of its attacks. If the ability on the table has a little dash next to it, then it doesn’t affect how well it can kill players and really, who cares about anything that’s not doing that?
The table on page 277 is also significant, as it describes the mathematical effect damage resistance and immunity has on a creature’s HP total. Removing such abilities without adjusting the creature’s hit points will result in a creature less threatening than intended.
Calculations become more difficult when spells and similar effects require adjustment. The easiest method, if possible, is to attribute the spell to a mundane or environmental effect. A so-called smoke bomb might be an excuse for a non-magical creature to acquire the effects of the Invisibility spell. The attacks from eldritch blast could be attributed to a repeating crossbow.
Less precise but theoretically equivalent is to take the damage that would have come from a spell and distribute it among the combatants. The average fireball will do 28 damage to 3-4 creatures. Of those creatures, it is reasonable to assume half will make the dexterity save, putting the average damage per creature at about 20. 20 is well within the most common values of a roll of 3d12. If a creature has 3 attacks available to it through multiattack or dual wielding capability, adding 1d12 to the damage for each attack will provide a quazi-equivalent increase in damage output to make up for the absent fireball spell. It is not guaranteed damage like a fireball, but the limited chances to cast spells and the likelihood that an optimal fireball is not repeatable (players will tend to scatter after the first example is provided) theoretically offsets the net effect of missed attacks.
So obviously when you’re making these changes, even if you use the formulas in the DMG, your mileage will vary. If you’re coming up with a horde-type creature, it might be good to throw a smaller group at the party first to judge how much trouble they’ll be. If you want two of them to be a small speed bump for the party and they turn out to be a full-on roadblock you may want to tone them down before a big fight.
Also, pay attention to the increases you’re making, especially if you’re tinkering with AC. If you increase AC to boost the CR level or because you’re removing abilities and it starts heading north of 20, it may be literally impossible for some of your players to hit the creature.
If you have issues with metagaming players where, for example, you say “you see a troll” and someone starts immediately encouraging everyone to light it on fire without so much as a nature check, adjustments like we talked about can throw them off their game. Maybe your troll doesn’t have regeneration and just has more hit points. Or, don’t call it a troll. Congratulations, you all found bigfoot, and now it wants to beat you to into mash, roll initiative. You get what I mean.
For those of you who want examples or more detail, our web wizard Gath Memvar wrote a guest blog about this very topic, so go check it out!