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I always assumed the difference between Beasts and Monstrosities was very simple: beasts are natural creatures that exist in our world, monstrosities are unnatural creatures that do not fit into any of the other categories. However, I was thinking about it and I realized some things that are classified ‘Beasts’ would be monstrosities by that definition, such as giant fire beetles.

The Monster Manual defines beasts as

non-humanoid creatures that are a natural part of the fantasy ecology.

and monstrosities as

monsters in the strictest sense- frightening creatures that are not ordinary, not natural, and almost never benign.

Is the distinction, then, simply one of origin? A fire beetle is a beast because it evolved naturally, while a Roc is a monstrosity because it was created directly by a Giant? This argument does not hold if you look at the roper, whose flavour text states

The roper is an evolved, mature form of piercer.

Is it one of alignment? A roper is a monstrosity because it is neutral evil, and a giant fire beetle is a beast because it is unaligned? But a roc is a monstrosity, and is also unaligned.

What, then, makes a creature such as a roper or roc a “monster in the strictest sense”, and a giant fire beetle or a stirge a “natural part of the fantasy ecology”?

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4 Answers 4

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Your question is looking for a definition beyond the definitions provided in the rules. There isn't one. Creatures are the types they are because that's how they've been defined in the rules.

The Rules

The terms "Beast" and "Monstrosity" are individual examples of "creature type", which is explained in the Basic Rules .

For beasts it says:

Beasts are nonhumanoid creatures that are a natural part of the fantasy ecology. Some of them have magical powers, but most are unintelligent and lack any society or language. Beasts include all varieties of ordinary animals, dinosaurs, and giant versions of animals.

For monstrosities it says:

Monstrosities are monsters in the strictest sense--frightening creatures that are not ordinary, not truly natural, and almost never benign. Some are the results of magical experimentation gone awry (such as owlbears), and others are the product of terrible curses (including minotaurs). They defy categorization, and in some sense serve as a catch-all category for creatures that don't fit into any other type.

But what's the difference between beasts and monstrosities?

That's it, what the definitions say, that's the difference.

There is no further explanation for what makes some things beasts and some things monstrosities. Furthermore, the rules do not provide further detail of what "monster in the strictest sense" and "a natural part of the fantasy ecology" mean, beyond what those phrases mean in everyday English. You can certainly look at the categories and at examples and look for patterns, but in the end, the rules say what the rules say.

The usefulness of creature type

It's pretty clear the usefulness of creature type. We can then have rules that say "druids can shapeshift into beasts", and the spell planar binding can "bind a celestial, an elemental, a fey, or a fiend". The basic rules say "certain spells, magic items, class features, and other effects in the game interact in special ways with creatures of a particular type." But that's not what you asked. You want to know why some creatures are thrown into one bin, and why some are thrown in another.

The binning problem

The rules categorize some creatures one way, some another.

Examples of beasts are various dinosaurs, brown bear, deep rothe, spider king.

Examples of monstrosities are aeorian absorber, assassin bug, death dog, hippogriff, winter wolf.

Generally, what are listed as beasts seem close to beasts in the real world, and what is listed as monsters seem, well, monstrous. You can look at the descriptions of the creatures, and look at the definitions, and either agree or disagree with the designers' decisions. While most people might agree on many examples, there could well be cases where a creature could reasonably be classified more than one way. But those would be subjective judgement calls.

In the end, we have to conclude that at some point content designers examined the creatures and assigned a type, but unless definitive statements can be found, the "why" remains a question of unanswerable designer intent. Metaphorically, we can imagine that, having come up with the definitions above, they examined each creature as it was being added to the 5e rules, and said, hmm, this looks more like a beast, this is obviously a monstrosity. Maybe they argued about it. There's nothing in the rules that defines the definitions beyond the definitions. Without statements outside of the rules, we don't know.

The challenge of categorization is not unique to D&D. There's even a whole Wikipedia article on it. It's useful to divide things into categories, but categorization itself is a simplification. In the end, you define bins, then you throw things into the bins, then you argue about it. Look at taxonomy. Taxonomists argue endlessly about what goes into which bin.

Making your own monster

The DMG provides guidance for creating your own monster. In Chapter 9: Dungeon Master's Workshop, Creating a Monster, Step 3. Type, it says:

A monster’s type provides insight into its origins and nature. The Monster Manual describes each monster type. Choose the type that best fits your concept for the monster.

In other words, look at the bins, look at the monster, throw it in one of the bins.

History of creature type

Finally, the article Creature type in the D&D Lore wiki provides a history of the concept of creature type, which is interesting, but does not provide much elucidation on what makes a creature one type and not another.

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    \$\begingroup\$ +1 I think it is an absolutely fair answer, and have no idea why someone would downvote it as "not helpful". \$\endgroup\$ Mar 13 at 19:57
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    \$\begingroup\$ I downvoted this answer and will not accept it for the reason that it does nothing to answer the question but restate quotes I already stated in my question. I am not trying to be rude, I just fail to see how people could think this is a helpful answer… \$\endgroup\$ Mar 13 at 22:47
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    \$\begingroup\$ Hmm. Can't work on it now, but when I can, I'll see what I can do to improve it, or perhaps someone else will come up with something more useful. \$\endgroup\$
    – Jack
    Mar 14 at 1:05
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    \$\begingroup\$ @TheDragonOfFlame Your core assertions in your question are wrong. Giant Fire Beetles are indeed a natural creature that live underground. Ropers are apparently not natural or ordinary regardless if they are the mature form of piercers. I think Jack has perfectly given you the definitions. There's no answer beyond that. \$\endgroup\$ Mar 14 at 7:03
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    \$\begingroup\$ @TheDragonOfFlame I've tried to improve the answer. Maybe I've made it worse. It's possible that your question is really one of designer intent, not one of rules. Without statements outside of the rules, which we find on many subjects, we can only speculate about designer intent. Some of the most interesting questions are about designer intent. Why don't wizards have healing spells? You can speculate all sorts of great reasons for that, that might make sense: "game balance", "arcane energy doesn't heal", "wizards are mean". But in the end, the rules only say what the rules say. \$\endgroup\$
    – Jack
    Mar 14 at 10:59
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Consider a druid's Wild Shape

and other ways to access creature abilities

As you cite, the Monster Manual explicitly explains that Beasts are "natural" while monstrosities are "not ordinary, not natural". Oftentimes monstrosities are fantastical beasts drawn from real-world mythology, so there is some coding there that has to do with theme, setting, and flavor. Depending on the nature of a DM's world, there might be more or less room for monstrosities, either in the world as a whole or in certain areas - their lack can make an area seem more naturalistic, their presence can heighten the sense of fantasy.

While there appear to be many reasons for separating the two (and, for that matter, for specifying a difference between monstrosities and aberrations), one of the most practical / game design reasons has to be that of character access to special abilities. Simply put, monstrosities, as fantastical creatures, often times have special abilities that beasts do not, special abilities that might prove unbalancing if they were reliably available to characters, especially low-level characters. As the Monster Manual says

Certain spells, magic items, class features, and other effects in the game interact in special ways with creatures of a particular type.

A fundamental game design feature is that it is fairly easy for characters to take the form of beasts (as well as to communicate with them or summon them, see below). Groody the Hobgoblin, in their answer, mentions Polymorph, a 4th level spell that is typically available to a 7th level caster. Far sooner than this, though, druid characters have access to Wild Shape. Beasts might have more naturalistic abilities like knocking opponents prone or pack tactics, or they might have swimming or flying speeds (which Wild Shape carefully limits to higher levels), but they don't generally have features out of balance with other options available to a second-level PC.

Without the distinction between Beasts and Monstrosities, however, or were Wild Shape to permit taking the form of a monstrosity, consider what abilities would be accessible to a second-level Circle of the Moon Druid. Often time these abilities mimic what might be accomplished with level-appropriate spells, but could be used multiple times in an encounter without having to spend spell slots:

As a CR1/2 Rust Monster (and available to all druids by level 4)

Rust Metal. Any nonmagical weapon made of metal that hits the rust monster corrodes. Antennae. The rust monster corrodes a nonmagical ferrous metal object it can see within 5 feet of it.

As a CR1 Death Dog:

If the target is a creature, it must succeed on a DC 12 Constitution saving throw against disease or become poisoned until the disease is cured. Every 24 hours that elapse, the creature must repeat the saving throw, reducing its hit point maximum by 5 (1d10) on a failure.

At 6th level, a Circle of the Moon Druid can wild shape into CR2 beasts. If this included monstrosities, they could add the following abilities,

As a CR2 Carrion Crawler:

the target must succeed on a DC 13 Constitution saving throw or be poisoned for 1 minute. Until this poison ends, the target is paralyzed.

As a CR2 Ettercap:

The creature is restrained by webbing.

As a CR2 Mimic:

Shapechanger. The mimic can use its action to polymorph into an object or back into its true, amorphous form... Adhesive (Object Form Only). A Huge or smaller creature adhered to the mimic is also grappled by it (escape DC 13). Ability checks made to escape this grapple have disadvantage. False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an ordinary object. Grappler. The mimic has advantage on attack rolls against any creature grappled by it.

At seventh level, any druid (as well as bards, sorcerers, and wizards) gains access to the polymorph spell, allowing creatures with a flying speed, which the Circle of the Moon druids can then wild shape into at level 8. Considering just monstrosities that then would be available for wild shape, we can add the

CR1/2 Cockatrice

the target must succeed on a DC 11 Constitution saving throw against being magically petrified. On a failed save, the creature begins to turn to stone and is restrained.

and the CR1 Harpy

Every humanoid and giant within 300 feet of the harpy that can hear the song must succeed on a DC 11 Wisdom saving throw or be charmed until the song ends.

Of course, by the time a druid caster gets polymorph, they can start making themselves or party-members into creatures of far higher CR than 2, meaning monstrosities with far more potent special abilities would be available if permitted.

I have limted myself in these examples to just those monsters within the Basic Rules and Monster Manual, that is, those that were official at the time the designers made the distinction between beasts and monstrosities. Since then, many others have been added, such as the young basilisk from Out of the Abyss. Since the distinction already exists, however, new beasts and monstrosities can be added to the game without affecting the balance of the classes so long as the designers keep in mind the principle that powerful special abilities are better kept to monstrosities.

When characters are not actually becoming beasts, they could be speaking with them to gain their favor (Speak with Animals, available at 1st level to Bards, Druids, and Rangers, as well as to certain Clerics and Paladins), or even summoning them as combat allies (Conjure Animals, available at 5th level to druids and later to rangers). Consider a 5th level druid conjuring four cockatrices with a single spell, getting four chances a round to turn opponents to stone. These spells are reasonably balanced when applying them to just beasts; if they could equally affect monstrosities, that would greatly change the power of the druid class with relation to the others by making many more special abilities either available or avoidable.

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  • \$\begingroup\$ You have a point. But the Stench Kow can poison every creature within 5 feet, and the roc is still just a big bird. \$\endgroup\$ Mar 14 at 14:18
  • \$\begingroup\$ @TheDragonOfFlame Stench Kows are classed as beasts, true, and within the CR range - but since they are native to the lower planes it is doubtful most low-level druids have seen one. Rocs are just really, really big birds and I think could easily be classed as beasts. IIRC their origin is in the Sinbad stories (the sailor, not the comedian), so that may be why they are considered fantastic enough to be monstrosities. Of course, at CR11, they would not be eligible for wild shape in any event. \$\endgroup\$
    – Kirt
    Mar 14 at 17:01
  • \$\begingroup\$ I assume Roc being a Monstrosity was an issue of Polymorph balance for lvl11 and higher PCs. It's a huge pile of hit points (nearly twice a T-Rex), and strong in combat, and gargantuan size. And has 120ft fly speed, carrying a large party for an hour with one spell (instead of multiple PCs needing to be giant eagles with 80 ft fly). (Polymorph does not require having seen the beast, unlike Wild Shape. So new books with beasts like CR10 Sky Leviathan (Plane Shift: Kaladesh) rather mess up that balance, if a DM allowed them in other campaigns. Or CR12 Traxigor (casts 18th level spells!) \$\endgroup\$ Mar 15 at 14:57
  • \$\begingroup\$ But yeah, there are still only 2 odd high-CR beasts above T-Rex, both from settings / modules, not things like Volo's Guide to Monsters. Overall 100% agree with Polymorph / Wild Shape balance being key factors. (And good point about Speak With Animals / Conjure Animals, although CR1/4 Velociraptor from Volo's having 2 decent attack makes it very strong for use with Conjure Animals. e.g. on an episode of the actual-play show Dimension 20: The Seven.) \$\endgroup\$ Mar 15 at 15:03
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    \$\begingroup\$ @PeterCordes I can certainly see the Roc being made a monstrosity to keep level 11's from polymorphing into it. As far a Traxigor, though, that is not a kind of creature, it is a specific NPC from descent into avernus - an archmage who was permanently transformed into an otter. You could no sooner polymorph into 'a traxigor' than say 'I want to polymorph the party fighter into a druid'. \$\endgroup\$
    – Kirt
    Mar 15 at 18:29
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It is a label chosen by the game designers

In 5e, creature type is just a label used for other game features to interact with. The Monster Manual explains this on page 6:

A monster's type speaks to its fundamental nature. Certain spells, magic items, class features, and other effects in the game interact in special ways with creatures of a particular type. For example, an arrow of dragon slaying deals extra damage not only to dragons but also other creatures of the dragon type, such as dragon turtles and wyverns.

Other than earlier editions of D&D, there are no overarching attributes that monsters of a specific type share. You can see this for example with undead. In 3.5, all creatures of the undead type shared certain characteristics, such as hit die, darkvision, immunities. All undead were immune to mind-affecting effects.

In 5e, this is no longer the case. Each monster is designed individually, and the creature type carries no other unifiying meaning than providing a creature type that may interact with other game features. That all undead are immune to poison is a feature of this being written into each individual description, not an effect of the creature type. If it were left off for one of them, it could be poisoned. So the type is just a label, nothing more.

Interacting effects

The entirety of the types in question is defined by the write-ups cited by Jack, and, importantly, by the other game features that reference them. For example, Polymorph can only polymorph a creature into a beast, not a monstrosity.

There can not be a comprehensive listing of such features, as the list will expand as new books are published for the system. However here are the ones in the PHB for beasts :

  • Druid's Wild Shape and Nature's Sanctuary, Gnome's Ability to speak with small beasts, Nature Domain's Charm Animals and Plants, Ranger's Companion or Favoured Enemy, Transmutation Wizard's Shapechanger
  • Spells: Animal Friendship, Animal Messenger, Animal Shapes, Awaken, Beast Sense, Conjure Animals, Dominate Beast, Locate Animals or Plants, Polymorph, Simulacrum, Speak with Animals

Compare this to those referencing monstrosities: these are merely one of the options for favoured enemies for Ranger.

As Kirt points out, a possible reason why something unusual is assigned to be a monstrosity then is: exotic monsters have powerful abilitities that can be game breaking if made accessible to player characters. Most spells and featurs are limitied to beasts, so labeling those as monstrosity does block players from accessing them. It is a tool for game balance.

Unusual beasts

Looking at the beasts, nearly all of them are animals or prehistoric animals that have counterparts in the real world. The only exceptions in the Monster Manual appear to be: Giant Fire Beetle, Stirge, Blood Hawk, Flying Snake, Dire Wolf, and Giant variants of normal animals. It is harder to understand why these monsters were not also classified as monstrosities -- as some of them like the Stirge have pretty unusual special abilities.

To unearth designer intent information why any of these unusual monsters was classified as a beast being "a natural part of fantasy ecology" rather than a monstrosity would need this information to exist somewhere in an interview. Maybe to convey that they would not be malevolent, or maybe to provide them as cool options for PC abilities like Druids Wild Shape, or Ranger's Animal Companion? Absent published statements we can only speculate.

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    \$\begingroup\$ This is kind of a 'spot the difference' answer, but do you have anything to back up the assertion that it is just a label? By extension with no real thought from the devs on why or what is what? \$\endgroup\$
    – SeriousBri
    Mar 13 at 19:46
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    \$\begingroup\$ I suspect the right answer is historical, lots of these things came from 1e, had meaning, and now are just vestigial. \$\endgroup\$
    – SeriousBri
    Mar 13 at 22:32
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    \$\begingroup\$ The Flying Snake is actually a real-world animal (nationalgeographic.com/animals/reptiles/facts/flying-snakes). Fire Beetle also exist (although not giant ones), Blood Hawks could exist (those are just normal hawks, but bigger and with pack tactics). Really, this list could be just "Stirge and bigger versions of real animals". \$\endgroup\$ Mar 14 at 11:48
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    \$\begingroup\$ @AnneAunyme, nice link. The flying snakes in the MM are a bit of a different "beast", in that they have full flight, but so do many other beasts, so no issue. I agree, it is mostly the stirge and giant animals, and maybe because giant animals differ not in abilities, they are relatively safe to use for PCs as higher level options. \$\endgroup\$ Mar 14 at 13:36
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It's vague and unclear

If we limit ourselves to reading the actual rulebooks of 5th edition, then you have quoted the relevant text. There's no clear distinction about what is a monstrosity and what's a beast beyond a vague "not truly natural", which brings up a question of what "natural" even means in a world where magic is a reality and sometimes acts on its own, without a sapient agent.

If we widen our net a bit and look at the greater history of D&D, the group of creatures now called "monstrosities" includes many creatures that were once referred to as "magical beasts" or "monstrous humanoids". Both categories, generally speaking, included creatures twisted or changed by magical meddling, whether by a magic user (on purpose or by accident), or due to the vagaries of uncontrolled or "wild" magic, planar effects, and other quasi-natural events.

However, the rules have never really been particularly coherent on the question of why certain creatures fall into certain types. The monstrous humanoid and magical beast types in particular have historically been a bit of a "miscellaneous drawer" for creatures that just don't seem to fit into any of the other types, but there is certainly an inherent arbitrariness in deciding that an orc is humanoid enough to be a regular humanoid but a minotaur isn't.

Ultimately there isn't a good answer to this because the creature types just aren't defined that well, and Monstrosity is less defined than most.

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