How to Make a D&D Monster

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This article first appeared on D&D Beyond. I’ve stripped most of the references to the D&D Beyond to keep the advice here more universal and streamlined. If you want advice on how to build a background specifically in D&D Beyond, check out that version of the article.

There’s nothing more satisfying than dropping an original monster on an unsuspecting group of players. While trolls, beholders, mind flayers, and ancient red dragons are great, those monsters have been around for decades. Players know what to expect when encountering them. Veteran players quake when a new monster hits the table, because a fresh creation brings an extra element of terror on top of claws and jaws: fear of the unknown.

I’m here to help you bring that fear to your players. Building new creature from scratch is a complicated task. That’s why I’m going to walk you through the process of monster design step-by-step.

Before You Start, Ask the Important Questions

Before you begin to design any new element of the game, don’t forget to ask these three questions, the importance of which are discussed in my backgrounds post:

  • What do I want to make?
  • Does my creation already exist as official D&D content?
  • Can I reskin or tweak another creation to suit my needs?

If the monster you’re considering designing doesn’t already exist and can’t be built by tweaking an existing creature, it’s time to design your own.

Designing Monsters

The Dungeon Master’s Guide provides guidelines for monster creation, which are great. I’ll expand on what’s provided and the steps in my process will vary a bit to give an even more in-depth look. All monsters have the following components you need to design:

  • Story
  • Size, type, and alignment
  • Challenge rating
  • Ability scores and modifiers
  • Armor Class
  • Hit points
  • Speed
  • Saving Throws
  • Skills
  • Damage resistances, immunities, and vulnerabilities
  • Condition immunities
  • Senses
  • Languages
  • Traits
  • Actions
  • Reactions
  • Legendary Actions
  • Lair Actions

For this article, I wanted to show you how to create every aspect of a monster and build an expected terror for my players, so I settled on using a legendary ooze I named the blood marmalade as an example.

Step 1. Story

Let your imagination run wild! What makes your creature different from all others. Open with a paragraph that gives a general overview of the monster. This paragraph describes where the monster lives, what the monster looks like, and how they fit into the larger world. Subsequent paragraphs should dive deep into specific story aspects of your monster. Start each new story aspect section with a bold and italic phrase that sums up that detail of your monster, so a DM skimming the passage can say, “Ah yes! I remember that the blood marmalade is an intelligent ooze that devours knowledge!” Each aspect of your monster should include a good story hook that helps GMs work the monster into their stories. In addition, you’ll want to include a little information on your monster’s physiology if they don’t require food, water, or sleep. Here’s what I wrote for the blood marmalade:

Thousands of years ago, a mad drow wizard named Maroc the Rotten became obsessed with creating a new ooze that could reason and carryout orders. His experiments resulted in the former, which meant Maroc never achieved the latter. His creation, a sanguine goop that preferred to take the vague shape of a humanoid, reasoned its way out of captivity and devoured the mage. The first blood marmalade traveled out into the Underdark, seeking more victims before it multiplied.

Devourers of Knowledge. Blood marmalades are intelligent oozes that gain the memories and knowledge of any creature they devour. Their hunger for flesh is only exceeded by their hunger to know more than any other creature in the world. They set elaborate traps for humanoids, particularly wizards, and try to draw sapient creatures into their lairs with tempting offers of treasure and lost tomes. Any intelligent or fleshy organisms near blood marmalades do not last long, but the odd monsters keep mindless oozes as guards.

You Are What You Eat. Blood marmalades can take on the appearance of any humanoid creature they consumed. They use the visage of their former victims as disguises to lure new meals into their homes and travel among the living to enact their plans.

Maroc’s Madness. Because all blood marmalades are descended from the original that consumed Maroc the Rotten, all have a touch of the wizard’s madness and malevolence. They delight in torturing their victims (by appearing as loved ones the ooze devoured if possible) before consuming them. Blood marmalades claim agony and fear make their prey more delicious.

Ooze Nature. An ooze does not require sleep.

Step 2. Size, Type, and Alignment

How big is your monster? What’s its type? What’s its alignment? Keep in mind a creature’s size affects its hit points (more on that later) and creatures, unlike player characters, can be unaligned. With those caveats, the choices are yours. What makes sense for your creature?

The blood marmalade is a Medium ooze with a chaotic evil alignment.

Step 3. Challenge Rating

Before you start getting into the numbers of your monster, you need other monsters to balance it against. Choose the challenge rating you want for your monster first and then design to that challenge rating rather than trying to figure out the number after you’ve designed the rest of the creature. You will be able to compare your beast to other creatures of similar challenge ratings and charts in the Dungeon Master’s Guide if you settle on a challenge rating at the start.

The blood marmalade has a challenge rating of 10 because there aren’t any oozes with a challenge rating that high in the Monster Manual and I want to surprise my players.

Step 4. Ability Scores and Modifiers

Your monster needs ability scores just like a player character. Remember 10 represents the score of an average human and 20 is the peak of human achievement. Use those as a baseline, and look at other monsters of the same challenge rating, size, and type in the Monster Manual to get an idea of your creature’s statistics. For instance, I want the blood marmalade to be just as strong and tough as gelatinous cube, so I gave it a Strength score of 14 and a Constitution score of 20. The blood marmalade is as smart as a mind flayer, so I gave the creature an Intelligence score of 19. Since my ooze is an outlier when it comes to creatures of the same type, I gave it a higher Dexterity, Wisdom, and Charisma score than other oozes.

Step 5. Armor Class

A monster’s Armor Class is calculated the same way a player character’s is, by adding 10 to the creature’s Dexterity modifier. Compare this number to other creatures of the same challenge rating and type. You should also refer to the Monster Statistics by Challenge Rating table in chapter 9, “Dungeon Master’s Workshop,” of the Dungeon Master’s Guide. The table is a solid guideline, but not gospel. You can find outliers for all statistics throughout the Monster Manual that don’t come close to the table’s numbers like the demilich, mind flayer, and pixie (all of which have lower hit points for their challenge ratings offset their powerful spellcasting abilities among other strengths).

If you want to increase your creature’s AC, you can add as much to it as you like to make it balanced by giving the creature natural armor or a suit of armor from chapter 5, “Equipment,” in the Player’s Handbook or Basic Rules. If you raise your creature’s AC, keep in mind that the tarrasque and Tiamat, fifth edition D&D’s toughest and most-difficult-to-hit official creatures, have an AC of 25.

If your creature’s AC is too high, give the creature a lower Dexterity score or leave its AC as is and balance for it being harder to hit by giving it less than average hit points (or another weakness somewhere down the line).

Step 6. Hit Points

For hit points, you’ll want to check the Monster Statistics by Challenge Rating table as well as other monsters of the same challenge rating and type as your original creature as you did with AC. Once you have a good range of hit points, figure out how many Hit Dice your creature needs to get to your desired total. As the Dungeon Master’s Guide points out, creature Hit Dice are based on size. To figure out a creature’s hit point total, use this equation: hit points = Y x (Hit Dice average + Constitution modifier). Y equals the number of Hit Dice used.

For the blood marmalade, I looked at many other CR 10 creatures published by Wizards of the Coast. White Maw (an ooze) from Dead in Thay in Tales from the Yawning Portal had the most hit points at 217 and Madam Eva from Curse of Strahd has the fewest hit points at 88. Most of the monsters from other sourcebooks fell between 135 and 184 hit points (fewer than what the Monster Statistics by Challenge Rating table recommends). I want the blood marmalade to be a bit tougher than average because of its low AC. I first figured out its Hit Die size, which is d8 given its Medium size. The average of a d8 is 4.5 and the blood marmalade’s Constitution modifier is +5, so the blood marmalade gets 9.5 hit points for every Hit Die it has. If I give the ooze 20 Hit Dice, that brings its total to 190, which seems perfect. Its hit points are expressed as 190 (20d8 + 100).

Step 7. Speed

Compare your monster’s speed to others of its challenge rating, type, and size. Give it any special movements speeds, like climbing, that you want it to have. Some special movement speeds, like burrowing or flying, can affect a creature’s challenge rating at lower levels, but at higher levels, most player characters have powerful enough spells or magic items to make those speeds less of a problem.

Most oozes are slow and can climb. The blood marmalade is a special kind of powerful (there aren’t many official oozes with CR greater than 4), so I’m going to give it a fast-for-an-ooze movement speed of 30 and a climbing speed to match.

Step 8. Saving Throws

You don’t need to add saving throw proficiencies if it doesn’t seem right for your creature or if the monster already has many powerful ability scores. Leave at least one save weaker than the others to give your creature a little realism and not frustrate your spellcasting players as the creature succeeds on save after save. Even the tarrasque and Tiamat aren’t as good with Dexterity saving throws as they are with others. (Note that the monster’s proficiency bonus is based on its CR and can be found on the Monster Statistics by Challenge Rating table in the Dungeon Master’s Guide.)

The blood marmalade is already set with most of its ability scores, but given the fact that it absorbs memories, I’m going to boost its Wisdom saving throw as a reflection of that.

Step 9. Skills

Like saving throws, your monster doesn’t need to be proficient in any skills, only the ones that make sense. Don’t be too worried about balance here. A few skill bonuses don’t make or break a creature, unless they have a feature tied to one of the skills (like Sneak Attack and Stealth) and even then, it’s likely the skill boost is warranted to make the ability work.

For the blood marmalade, I’ve given it proficiency in Deception so it can pretend to be something it’s not.

Step 10. Damage Resistances, Immunities, and Vulnerabilities

Your monster does not need any damage resistances, immunities, or vulnerabilities. Do whatever makes sense for the story. To get some ideas, look at other creatures of the same type. One to three resistances or immunities don’t change a monster’s challenge rating, but four or more should make you think twice about adjusting another aspect of the monster (like its hit points) to compensate. The exception to this rule is resistance or immunity from bludgeoning, piercing, and slashing damage from nonmagical weapons. At lower levels such a strength is difficult to overcome no matter what other resistances a creature the creature has, but by a party of level 5 characters can cast a spell or two to overcome the resistance.

Unlike previous editions of D&D, vulnerabilities make few appearances in monster stat blocks in the game’s current iteration. Use vulnerabilities with caution, since double damage makes some (or all depending on the party and damage type) player characters twice as strong.

The blood marmalade is a super strong ooze, and as such, I gave it acid damage immunity.

Step 11. Condition Immunities

Your monster does not need condition immunities. Stick to what makes sense and look at other creatures of the same type. Some creature types (like oozes) have many condition immunities because they make sense with the creature’s story. Something that’s formless is never prone, something that’s mindless can’t be charmed or frightened, and something that can’t see or hear (but uses other senses) can’t be blinded or deafened. Those all make sense for an unintelligent ooze. Figure out what conditions should not apply to your creature and only add more condition immunities beyond what makes sense to compensate for the creature lacking in another area, like AC, hit points, etc.

Since the blood marmalade is an intelligent ooze that can see and hear things, it has far fewer condition immunities than other oozes. (Such is the price of sapience.) It is still immune to the prone condition and exhaustion, because it still has the physiology of an ooze.

Step 12. Senses

Your creature should at least have a passive Perception score (calculated the same way it is for player characters). If your creature has any extra senses like blindsight or darkvision add them as well. Most senses won’t break the game. Add whatever makes sense for your creature’s story.

Unlike other oozes, the blood marmalade does not have blindsight, but it can see and lives in the Underdark, so I gave it 120-foot darkvision.

Step 13. Languages

What languages, if any, does your creature read, speak, and understand? You can’t break the game here so add as many or as few languages as you like. Feel free to put any restrictions or story elements into this description. For instance, the blood marmalade speaks “Common, Elvish, Undercommon, and the languages of any creatures it has consumed.”

Step 14. Traits

What makes your monster special? Some creatures, like tyrannosaurus rex, have no special traits. Others, like the vampire, have many. From spellcasting to walking on webs, anything special your creature can do that is not an action or reaction should be here.

If you want to use a feature that another monster has, use the same name and just tweak the feature’s wording to apply to your monster. This helps DMs everywhere because when I see the Pack Tactics feature in a stat block, I know what it does without having to read the rest of the description because I’ve seen the feature on other creatures before. That’s what I did for the blood marmalade’s Amorphous feature taken from the ochre jelly and the Legendary Resistance feature taken from the ancient gold dragon.

I did have to create the Knowledge Consumed feature from scratch. I used the Wizards of the Coast style to make sure this feature plays nice with other rules in the game:

Knowledge Consumed. When the marmalade kills a creature with its slam attack or when it consumes a corpse that has been dead for less than 24 hours, it gains all of that creature’s memories and learns everything the creature knew, including any languages. If the creature is a Medium or smaller humanoid, the marmalade can also take on that creature’s appearance using Change Shape.

These three features together don’t change the ooze’s power level beyond CR 10, since they don’t increase its raw power much. Legendary Resistance is the blood marmalade’s most powerful mechanical feature and has a limited use.

If you add a lot of features to your creature, consider how they change the creature’s power level. The power to cast spells like a level 14 wizard or a big boost to damage mean you probably should increase your creature’s challenge rating or reduce its hit points, AC, or damage output. There’s a reason wizards don’t have as many hit points as a fighter.

Step 15. Actions

Your creature’s attacks and other actions should go under this heading. List them in this order:

  • Multiattack (if the creature has it)
  • Melee and ranged attacks in alphabetical order
  • Other actions in alphabetical order

The Dungeon Master’s Guide shares how to calculate the exact attack bonuses and DCs for monster actions. Once again, follow the guidelines on the Monster Statistics by Challenge Rating table and look at monsters of a similar challenge rating to get an idea of what a monster’s average damage output should look like. If a monster is able to cast big damage-dealing spells, do extra damage under specific circumstances (like Sneak Attack), or can dish out a lot of non-damaging but debilitating effects (like petrification), consider give it a lower than average damage output for its regular attacks. Use creatures of a similar challenge rating that cast a lot of spells or those that deal out strange effects as your guide for this.

It seems many challenge rating 10 creatures deal between 2 damage (Madam Eva’s dagger) to 60 (the froghemoth’s two tentacles and a bite). Note the damage range is below that of the Monster Statistics by Challenge Rating table, because all challenge rating 10 monsters have some crazy features beyond damage. The blood marmalade is all about that damage from its slam attacks, so those are on the higher end of the spectrum. Then I also gave it a special acid spray action with a recharge (similar to a dragon’s breath weapon), to give it a ranged attack option and make the creature extra terrifying! Here are all of its actions:

Multiattack. The marmalade makes two slam attacks.

Slam. Melee Weapon Attack:  +6 to hit, reach 5 ft., one target. Hit: 12 (3d6 + 2) bludgeoning damage and 22 (4d10) acid damage.

Acid Spray (Recharge 5-6). The marmalade squirts acid in a 30-foot cone. Each creature in that area must make a DC 16 Dexterity saving throw, taking 33 (6d10) acid damage on a failed save, or half as much damage on a successful one.

Change Shape. The marmalade takes on the appearance of a Medium or smaller humanoid that has consumed (see Knowledge Consumed) or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is borne by the new form.

In a new form, the marmalade retains all of its statistics. It merely takes on the appearance of the humanoid.

Step 16. Reactions

Does your creature have a special reactions outside of opportunity attacks (like the noble’s Parry)? For the most part, reactions should not be as powerful as full actions. They’re usually defensive, like providing a quick boost to AC on a hit or a free movement when missed with a melee attack. If a creature’s reaction allows them to do more damage than a normal opportunity attack, there better be a good reason for it and balance somewhere else within the creature.

The blood marmalade has no special reactions for two reasons. First, I want to leave its reactions free to take opportunity attacks with their damaging slam. Second, the ooze also gets legendary actions and adding reactions in on top of everything else is just going to make the creature difficult to run at the table.

Step 17. Legendary Actions

Legendary actions are reserved for D&D’s scariest and most iconic monsters: dragons, beholders, liches, and unicorns to name a few. The blood marmalade joins these ranks!

When you design legendary actions, take a look at other creatures of similar challenge rating’s legendary actions to get an idea of how much damage and the effects these actions have. Like reactions, a single legendary action should not be more powerful than an opportunity attack, but many creatures can spend multiple legendary actions to gain a unique action that’s more powerful. Not all legendary actions need be attacks either, they could be movement-related or grant the creature a skill check, like the aboleth’s Detect.

The blood marmalade’s slam attack is a little too damaging to grant it as a legendary action, but I have some other ideas that I think are well-balanced.

Acid Spit. The marmalade chooses one creature it can see within 20 feet of it. That creature must succeed on a DC 16 Dexterity saving throw or take 16 (3d10) acid damage.

Command Ooze. The marmalade targets one ooze with a challenge rating of 4 or less it can see within 30 feet of it. The ooze can make one weapon attack as a reaction and gains advantage on the attack roll.

Absorb Ooze (Costs 2 Actions). The marmalade targets one ooze with less than 20 hit points remaining within 20 feet of it. The marmalade absorbs the ooze, destroying that creature and regaining a number of hit points equal to the number of remaining hit points the destroyed ooze had.

Step 18. Lair Actions

While many creatures have a lair, only a few are powerful enough to have lair actions (these creatures usually also have legendary actions). Include an opening paragraph or three that describes the environment where your creature makes its lair and the defense they have in place.

When it comes time to make lair actions, look at creatures of a similar challenge rating that have them (as you did with legendary actions). Lair actions are no more powerful than an opportunity attack. Use that guideline to help you create two or three lair actions.

Each lair also has at least three regional effects that occur within 1 to 6 miles outside of the creature’s lair. Have fun with these effects! These can be mechanically light and flavorful. If you do give a regional effect a hard mechanic, make sure it doesn’t add to the creature’s power rating and stays regional, like the Ki-rin’s ability to cast control weather.

Here’s the description of the blood marmalade’s lair:

Blood marmalades lair in the towers of wizards they murder and caves in the Underdark. They surround themselves with mindless ooze guardians they can control and make a point of being close enough to a busy road or city so that they can slip out into the night and hunt intelligent prey.

The walls, floors, and ceilings of a blood marmalade’s lair drip with a slippery mucus that begins to magically appear in the place after the ooze claims it as a home. The thicker this mucus, the longer the blood marmalade has lived in the lair.

Lair Actions

On initiative count 20 (losing initiative ties), the marmalade takes a lair action to cause one of the following effects; the marmalade can’t use the same effect two rounds in a row:

  • A 20-foot-square glob of mucus erupts from the floor within 90 feet of the marmalade. Each non-ooze creature that moves into or is in contact with that area of the floor when the mucus appears must make a DC 15 Dexterity saving throw. Creatures that fail are restrained. The mucus last until initiative count 20 of the next round.
  • The marmalade picks one creature it can see within 60 feet of it. A glob of thick mucus magically appear and fly at the creature’s head. That creature must succeed on a DC 15 Dexterity saving throw or it is blinded until initiative count 20 of the next round.

Regional Effects

The region containing a legendary marmalade’s lair is warped by the ooze’s unnatural presence, which creates one or more of the following effects:

  • Small lakes of red mud appear within 1 mile of the lair.
  • A thick red mist surrounds the area within 1 mile of the lair, making the area lightly obscured.
  • Oozes within 3 miles of the lair tremble with excitement and hunt in packs.

If the marmalade dies, any ooze packs immediately disperse and the other effects fade over the course of 3d10 days.

Step 19. Edit and Playtest

Now that you’ve created your monster, give it a once over. Read it out loud and edit. Even the most experienced designers need to edit their work. Then send your work to a friend to make comments. A second pair of eyes helps you understand if the design intent of your creature is coming through.

If you have the opportunity to playtest your new creature, take it! Nothing is a better test of your design work than actually seeing it in action. Plus it’s a great excuse to get friends together for a game of D&D! Change anything you think needs it after playtesting.

Step 20. Make Your Work Public

It’s time to make your work public! That means sharing the monster with your group, posting it to a blog, putting it up for sale on the DMs Guild, or on D&D Beyond.

Lucky for me the blood marmalade was accepted. You can find the final version here!

GO MAKE STUFF!

There you have it! A step-by-step process for creating a D&D monster. I can’t wait to see what people create. Share your creations with me on Twitter @JamesIntrocaso on in the comments below. Next week, I’ll show you how to make a new race!

If you like what you’re reading please follow me on Twitter, like World Builder Blog on Facebook, check out my podcasts, find my products on the DMs Guild, tell your friends about the blog, and/or leave me a comment and let me know you think. Thanks!

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