Monster Building 101: It’s Alive, IT’S ALIVE!

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Let me tell you a story that most GMs will be able to relate to.

The other day, I was working on an adventure for my home group. Now, I can’t talk in too much detail about it for fear that my players will read this article before they finish the adventure and ruin a surprise. Anyway, I found myself flipping through the Monster Manual, looking for something to fill out an encounter in a room that had a really thing I can’t talk about. And I realized I hadn’t given any thought to dinner for the night. Well, I decided it was a good night for this lemon and dill infused salmon I make in my steamer. But that would mean a trip to the store. So, I decided to put the adventure building on hold and head to the grocery store. There, I picked up a chunk of salmon, a lemon, and some fresh dill. But the store didn’t have any fresh dill. As a fun side note, I’ve been having a lot of trouble finding dill in Chicago. I don’t know why. But that aside, the store had no fresh dill. And ground up dill bits in one of those little spice jars wouldn’t work.

Now, dill is one of those tricky herbs. There’s nothing quite like it. Substituting for dill is damned hard. In fact, just to make sure, I pulled out my iPhone and did a quick internet search. Sure enough, everyone agrees, it’s dill or nothing. Now, ultimately, salmon works well with tarragon or thyme. The store didn’t have either of those fresh either. So I had McDonalds. Because, if dinner was going to be ruined, it was going to be Ruined with a capital ‘r’. I don’t handle disappointment well. I get spiteful.

At the same time, I’d been thinking about my monster and adventure thing. I couldn’t find just the perfect monster in the Monster Manual. But that was an easy fix. I’d just make my own monster. And then I found myself thinking that the adventure would actually work better if I customized several other monsters. So after I finished the McDonalds, I starting statting up some custom monsters. But I had to stop pretty quickly so I could go to the bathroom and suffer the consequences of McDonalds. I won’t go into details.

I found myself thinking about the dill problem. If I’d been a geneticist, I could have handled the situation easily. I could have just picked up a few herbs, taken them to my genetics lab, and grown my own custom dill. But I’m an accountant. And coming up with your own custom solutions in accounting usually ends up with the IRS throwing you in jail.

Fortunately, at least my adventure wasn’t ruined and didn’t land me in the bathroom for two hours. It came out really good. Because, while I can’t grow my own custom herbs, I can build my own custom monsters. I’m sure you were all hoping for an article about amateur genetics, but instead, we’re going to talk about custom monster construction in 5E today.

Why Now?

Why am I talking about this now? Aren’t I in the middle of a great series on building adventures? And aren’t I also in the middle of a big honking series about building a giant dungeon? Is now really the time to discuss how to populate your adventures with custom critters so that your fantastic adventure ideas aren’t hampered by the limited selections of same-ole same-ole monsters in that $50 tome? Note my clever use of sarcasm to illustrate my point.

Custom monsters are an extremely powerful tool. In fact, after actually knowing how to build a f$&%ing adventure, I’d say that it’s the most important tool in the adventure building toolkit. At least in D&D. Because D&D adventures always involve at least one good battle. And one of the things the designers of D&D actually did really well in the Dungeon Master’s Guide for 5E was to actually provide robust tools for building custom monsters. And when I say building, I mean Building with a capital ‘B’.

Now, we’re going to break this down into THREE lessons. Lesson one is about custom monster building the RIGHT WAY. That’s this one. Lesson two is about custom monster building in D&D 5E. Lesson three is about custom monster building in Pathfinder, because I don’t want to leave the Pathfinder folks out.

Why Skinjobs Suck

Let’s talk about skinjobs. No, I don’t mean the androids from the early 1980’s sci-fi classic Terminator (or whatever, I frankly don’t give a f$&%). I mean the skinjobs that most DMs online tell you are all you need. That is, reskinning monsters.

A skinjob or reskin occurs when you take a monster from the Monster Manual and use the monster’s stats, but you call it a different monster and change it’s appearance. So, it’s not a kobold, it’s a fiendish monkey creature that inhabits your little jungle temple. And it’s not a troll, it’s a giant gorilla that happens to be regenerate and have a weirdly inexplicable vulnerability to fire and acid.

Now, there is nothing inherently wrong with this approach except that it is terrible and it makes you a horrible GM and every time you do it, it makes Gary Gygax cry in gamer Valhalla. That’s right, you’re the reason Gary Gygax can’t enjoy a peaceful gamer afterlife with endless beer and 1d4+2 virgin valkyries.

Look, reskinning is an okay thing once in a rare while. It’s kind of like a dude wearing his sister’s underwear. It can get him through an emergency, but he doesn’t want to make a habit of it.

The thing with reskinning is that, ideally, theme and mechanics work together in a beautiful synergy. The whole becomes greater than the sum of its parts because of the way the two parts work together. So, sure, I could turn kobolds into monkey-beings that guard my monkey temple. But looking at some interesting furry mammals, I discover lemurs have tough bites and a powerful leap and they tend to mob prey. They also have a amazing climbing ability. Kobolds just have that mob thing. Think how much more more interesting my lemurians could be. The ceilings of my temples could be overgrown with vines and the lemurians could leap up to the ceiling, drop on invaders, and mob them to pull them down. There’s nothing quite like that in the Monster Manual.

And that sort of crap invites players to get creative. Maybe the fire wizard burns the vines so the lemurians can’t escape to the ceiling. I don’t know. Something. And the party stays close together so the lemurians can’t mob one party member. Or they retreat from the vine rooms.

When form matches function, the players can make educated guesses about tactics even before they see those tactics in action. Moreover, when the players are caught by surprise by some weird ability, instead of feeling screwed, they look at the creature and say “oh, yeah, that actually makes sense, should have seen that coming.” It empowers the players. A kobold in a monkey costume isn’t empowering.

Close Enough isn’t Good Enough

When D&D 4E hit the scene, one of the things that became popular was this crib sheet that let you slap together a quick-and-dirty monster by eyeballing the stats. All first level beasties should have an AC of 12, for example, or do 5 hp of damage with an attack bonus of +3. Whatever. Doesn’t matter the specifics. That got spread around. And it was utter crap.

Meanwhile, both Pathfinder and D&D 5E have these tables of expected stats by Challenge Rating. And the implication is that you can simply slap together a monster by picking a row on that table, giving it those stats, and calling it a day. And you can. If you want to suck.

Both Pathfinder and D&D 5E have a really beautiful (yeah, I said nice thing) internal logic to them, a consistency. And the players and the GM learn that consistency by using it over and over and over. And then, it gives them cues. If a monster normal-size is wielding a longsword, I know about how much damage that thing is going to do to me. At least, I can ballpark it. And this goes pretty deep. Deeper than you realize. If a monster is wearing light armor and it doesn’t have any sort of shell or scales or thick hide and I consistently miss on my attacks, the spellcaster is not going to throw anything that can be dodged. No Dexterity or Reflex saves. Why? The creature probably has a high Dexterity score and thus is really good at hitting the deck when a fireball goes off. And if the creature isn’t physically imposing, I’m more likely to succeed if I try to wrestle it or shove it around. Consciously or not, the players makes decisions based on all the cues you give them. And spellcasters especially rely on those cues, because most of their resources are limited, and they need to use the right tool for the right job.

It’s ESPECIALLY important if you’re ever going to share a monster beyond the table not to simply fake it. Because you never know who is using your stuff. Maybe it is some table of non-tactical fluffy gamers who don’t give a f$&%. Or maybe it’s a table of real players who play right and focus on decisions and choices, including those of a tactical nature. It actually takes nothing away from the fluffy players if the monster is mechanically consistent. The only reason people avoid it is because it’s tricky work.

Lazy GMs Need Not Apply

Long story short, if you’re lazy or impatient or just want to half-a$& things, custom monster building isn’t for you. You can do the skinjobs, you can do the close-enough, but frankly, why bother? Sure you can reskin a troll so that your players “won’t metagame and use its weaknesses,” but all that does is (a) prevent you from learning how to build GOOD monsters, (b) prevent you from learning how to build GOOD challenges without relying on surprise screw-jobs, (c) piss off your players, and (d) give you a monster you can only ever use once because after that the players will know their weaknesses and you don’t know how to handle it when players KNOW the weaknesses of a monster and exploit them.

Custom monster building is kind of like painting miniatures. Some folks do it to make their games better, right? But it’s a lot of work. And it’s something you kind of have to enjoy for its own merits. Frankly, most GMs never need to touch custom monster building. At all. But if you’re going to touch it, you need to understand it takes time and patience, there’s a right way to do it, and your efforts will get better with time and practice.

Monster Building Basics

First, last, and in between, Pathfinder and ESPECIALLY Dungeons and Dragons 5E give you some really GREAT tools to build monsters with. And they explain those tools really, really badly. Especially Dungeons and Dragon’s 5th Edition. Holy s$&% is that a mess of explanation for a really great set of tools. What that means is I’m going to f$%& with their process somewhat. I’m going to tell you a better process. So anytime I contradict something they say, f$&% them. I’m doing it better.

Let’s start with some basic rules. Or rather, let’s end with some basic rules. In the next installment, we’ll tackle the specifics of monster building in D&D 5E. And after that, we’ll make some Pathfinder beasts. So, you enjoy these quick tips and I’m going to have some salmon.

Understand the F$%&ing System

You cannot build a solid, consistent, well-designed custom monster without an understanding of the system itself. And I mean a good understanding. In D&D 5E for example, you’ve got to know how a saving throw DC is calculated (8 + Proficiency Modifier + relevant Ability Score Modifier). Same with Pathfinder (10 + half HD + relevant Ability Score modifier). You need to know what the components of an attack roll are and how damage is calculated. You need to know, in your system of choice, how skill bonuses are determined, and how many feats something gets, and what it means to be a monstrosity or not to have a Constitution score. You don’t have to be able to quote this stuff without reference to a book (though eventually, you will be able to), but you need to know where to find this information. And that’s tricky in both D&D 5E and Pathfinder. 5E is so poorly arranged it’s hard to find anything and building a monster requires three books. In Pathfinder, it’s easier and only takes two books, but they are massive books with lots of stuff in them.

Know Why You’re Building What You’re Building

You have to know why you’re doing what you’re doing. And I don’t mean “I want something new and unique here in this room,” or “I’m bored and want to build a monster.” Before you decide to build a monster, you’ve got to know what purpose the monster serves in the game. Now, I’ve seen a lot of custom monster stuff tell you that “you need a good concept.” That’s not true. You don’t need a good concept before you start building. Like, you don’t need to say “I need an animated statue here that contains the divine essence of a god and serves as the final guardian for a sacred site and has divine magic.” But you DO need to say “well, I’ve got a temple that needs a guardian thing.”

More specifically, you need to know what role the monster fills in the game. Is it self-sufficient or does it work as part of a group? If it’s part of a group, what does it do in that group? Is it just ground infantry, ranged support, leadership, whatever? What are its goals? What’s it trying to accomplish? How does it serve the game? And how powerful is it? In concrete game terms, that is.

“I need a final guardian for my temple, the last challenge of the adventure, and it alone has to try to drive off or defeat the party. It’s defensive by nature and should try to outlast the party while protecting whatever it protects. And it needs to be a difficult challenge for 4th level PCs. Let’s say CR 5.”


“I need little humanoid temple servants to serve the same ecological niche as goblins and kobolds. They work as a group and I should probably come up with a couple of different varieties. They should be monkey themed. They’ll be up against 4th level PCs, but individually, they aren’t very powerful. CR 1 tops so I can use lots of them.”

Figure Out Your Target Numbers

Monsters have a whole bunch of combat statistics, like attack modifiers, damage, armor class, saving throws, and hit points. You want to figure out roughly speaking where you need those numbers to be. We’ll come back to this in more detail in parts two and three because it’s quite system specific. But the thing is, you always want to work backwards into the creature. Basically, you want to do this in the complete opposite way you build a PC. Well, mostly. I’ll explain what I mean with the last bit:

Ability Scores Come Last

Your ability scores, regardless of the system you are working with, are the LAST THING you come up with. Not the first. The last. Well, among the last. Hit Dice also come pretty near the end. You might think that the ability scores are so central to your concept that you need to know those first. And it’s not bad to know that a creature is going to be strong or agile or smart or alert. But ability scores are the thing you have the most actual freedom with in either system. So, when you discover that your damage is coming up short, you can tweak it by giving the creature an extra two points of Strength. Now, that Strength increase is going to trickle back through to other things (like attack rolls or skill checks), but it’s that system that keeps your creature consistent so that players can decide that it’s too strong to shove or too agile to fireball.

Tweak, Tweak, Tweak

As you build your monster, you’re going to bounce back and forth a lot. You’re going to discover that the Constitution score you gave it puts it’s HP too high, so you have to take away a HD or two, which will affect its skill points and feats (maybe). Or the extra point of Strength gives it too much extra damage. So, you’re going to be fiddling a bit, especially toward the end, to make everything work. Just accept that.

Concepts Get Tweaked Too

So, my little lemurians might start out weak and agile, but during the tweaking phase, they might get stronger because of attack and damage roll calculations. That’s fine. I just have to be willing to make them stronger. Maybe instead of lemur people, they are baboon people. A little bit tougher than before.

The point is, your concept isn’t superior to the mechanics. Everyone thinks mechanics must serve the concept and any tweaking is always done to the mechanics. Well, that’s not true. It’s got to be able to go either way. Sometimes the needs of the game need to feed back up the assembly line and affect the concept, the fluff, the story. If you can’t get over that, if you are so married to your concepts that the idea of letting the game mechanics force a tweak, you can’t build custom content. Accept it.

Know When to Stop

In the end, though, you’re also never going to get it perfect. It’s never going to be one hundred percent dead on. The numbers won’t quite match. You’re going to be a little off here and there. And tweaking one thing will break another. There does come a point where you have to stop fiddling and accept that some part of it is going to be a little off. No system is perfect. Strive for precision, but have a reasonable tolerance for error.

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9 thoughts on “Monster Building 101: It’s Alive, IT’S ALIVE!

  1. Really looking forward to this. I made a -ton- of custom monsters in 3.5 D&D because it was fun and the system was set up to do it easily and systematically. In 5e I’ve made some homebrew stuff but it falls more into the “Close Enough isn’t Good Enough” category. Slap an AC, HP, AB, and damage on it and call it a day.

    I haven’t been good this edition about reading through the DMG to find all the information I need. In 3.5 all the advancement stuff was at the back of the monster manual so I could just look there. Consequently all that information made it by far my favorite and most used book.

  2. I can see where you are going with this. I think i’m going to wait for your excellent explanation before I rebuild my monster maker from the ground up.

    • I expect it will be relatively easy to apply the principles without much modification. I adapted his paragon monster rules to my 4e elites and solos with little effort, and they have worked brilliantly.

  3. Pingback: A Memorandum on Class Design: Milestones, Thematics, and Details | Loot The Body

  4. Ooooooh. I’m glad to find this; I’ve been struggling through trying to build a 5e monster, and it’s… well, a struggle. (I did have some success with a partial skinjob recently, in that I blended the statistics of one monster with a toned-down version of another monster’s actions to make a younger version of the latter. But the monster I want now does not lend itself to such approaches, so I look forward with interest to reaching the next entry in this series.)

  5. Yeah, I’m having a hard time making heads or tails out of the monster customization written in the 5E materials. It looks like they have a good system in there—if only I could figure it out.

    I feel I was able to build custom monsters WAAAAY easier in 3rd edition (I skipped 4th). I like 5E quite a lot, but am struggling trying to decipher what the game builders mean in the sections of towards the end of the DMG that detail how to build a custom monster. There’s charts and the content seems to conflict. Depending on how I read the charts my custom monsters end up with Challenge Ratings that are either WAY too High or WAY too Low. I end up just winging/skinning it, but that is frustrating as I intend to do some very large scale changes to monsters (re-writing dragons for my campaign) and I’d like to get a better idea of how to balance what I’m building.

    Perhaps my reading comprehension isn’t up to par, but I honestly think the explanations in the 5E DMG are pretty crappy.

    I do not understand the if/then ranges of charts for building monsters based on damage, AC, and Hit Points and how to figure out my Challenge Ratings. It seems like some elements should supersede others, but its not very clear. I’d love to see an example monster built with their rules and then check to see that it came out right (matches the MM). If I had an example. I think I’d be able to see what I’m missing.

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