Why does creature Type do nothing? Would the game break if it did?

[Malimar]

(I recognize that this question fundamentally betrays a "why isn't 5e just the same as 3.5e?" premise. Let's set that aside for now.)

In 3.5e, each creature Type had a list of qualities bestowed by having that Type. All Oozes and Vermin were Mindless; Undead and Constructs didn't need to eat, breathe, or sleep; Undead were healed by negative energy damage and harmed by positive energy healing; each Type had a specific hit die size and specific good/bad saves for all their racial HD, and so on. (I don't know anything about 4e.)

When they designed 5e, they kept the concept of creature Types, but they stripped away most everything it actually did, and now it affects only spells that target specific Types, Ranger Favored Enemy, Bane weapons... In short, Type doesn't do anything, and it only is done to by a few things. There's nothing that fundamentally makes an Undead distinct from a Humanoid. (I mean, I guess most (all?) Undead creature statblocks happen to have the Undead Nature trait making them not need to eat, drink, breathe, or sleep; many Types have such Nature traits listed in statblocks for all creatures of the Type; but why not centralize that by making it a feature of the Type and calling out exceptions in specific statblocks instead?)

Does anybody know, or have any speculation, why that decision was made?

Would it break anything if I were inclined to reintroduce Type traits? Starting with, say, damage Immunities and Vulnerabilities -- off the top of my head, make Undead Resistant to Necrotic and Vulnerable to Radiant; make Fiends Vulnerable to Radiant; make Celestials Resistant to Radiant and maybe Vulnerable to Necrotic (I dunno, I haven't fully fleshed out the idea yet, just making sure whether there are or aren't reasons I shouldn't bother). Potential pitfall is that change specifically would turns Paladins into Undead- and Fiend-smiting god-machines... but aren't they kind of supposed to be, by the lore?

[Beelzebub1111]

I think the choice was made to make things easier for new DMs. So they didn't have to remember a dozen different traits for each monster type, everything they need to know is in the statblock. The trait is effectively a tag so that they can add spells and abilities that affect them. (like turn undead or calm animal)

So it increases the length of the statblock but allows DMs to have all the materials they need for it at hand. of course it also creates a lot of backend work for people who want to make custom monsters or write their own encounters, but backloading a lot of the mechanical work onto the dm so the players don't have to think about it also a trait of 5e. "more freedom, less support"

[Amnestic]

It wouldn't 'break' anything really. Just so long as you still let rogues sneak attack undead/constructs without jumping through feat or alternate class feature hoops, it should be fine.

As Beelzebub said, the removal was mostly to streamline it for DMs - means you don't need to remember creature traits. They could have added those sorts of traits to every single statblock, but I'm guessing they didn't want to use all the ink+page space, so they only hit the high-notes when necessary.

Vulnerable being double damage is pretty potent though (and lopsided vs. Resistance, typically), especially when the numbers start getting bigger. If that's a concern, you could trade it out for something like

Radiant Weakness
The creature with this trait takes an additional 1d8 whenever they take Radiant damage.

But Vuln might work just fine too. No reason not to try it.

[Mastikator]

It would change very little. Almost every undead is either resistant or immune to necrotic, and has either vulnerability to radiant or some thing they no longer do if hit by radiant (vampires don't regen for example). Almost every construct does not need to eat, breathe, drink or sleep. Divine Smite already does extra damage to fiends and undead. Basically all of the creature type effects are moved into the creature stat block.

The stat blocks are bigger, but you have to remember less about the game when using a stat block. This is friendlier to newer DMs, and IMO better for all DMs since the reduced cognitive load means better DMing.

[Telonius]

Personally I suspect that it was for two reasons. First, to streamline things for DMs. Instead of needing to remember the rules for each type when you have a skeleton, or look up the type, all the relevant information is there in the statblock. (Personally I found it easy enough to memorize for 3.5, but I can understand that not every DM would have the same). So it is trying to minimize page-flipping. As far as that goes, if you can remember them without checking, it wouldn't really break anything.

Second thing, one of the things that 3.5 was criticized for, was having dozens of fiddly little effects on the same creature (whether from spells, types, class features, racial features, items...) So when they made the switch, a lot of the fiddliness (like DR 5/fire, or DR 10/magic) got thrown out or glommed together in Resistance or Vulnerability. Another big shift from 3.5 is that Resistance no longer turns 35 damage into 30 damage (5/fire) for a 10d6 fireball, it turns it into 17 damage (halved). And vulnerability no longer turns 35 Fire damage into 52 Fire damage (x1.5 in 3.5), it turns it into 70 Fire damage (doubled in 5e). So if you're going to be adding resistance and vulnerability back in for more creatures, realize that it's going to make things a lot more "swingy" - it's going to have much more of a mechanical impact that it would have in 3.5. Having the right spell available could trivialize the encounter, and not having the right spell (or worse, just "wrong" spells) could turn it into a much more dangerous fight.

[stoutstien]

I don't see why it couldn't be both. Too many cases of information being in only one place and if you miss it then it greatly swings the fit and feel of NPCs and underlying working if the setting.

[JonBeowulf]

It would change very little. Almost every undead is either resistant or immune to necrotic, and has either vulnerability to radiant or some thing they no longer do if hit by radiant (vampires don't regen for example). Almost every construct does not need to eat, breathe, drink or sleep. Divine Smite already does extra damage to fiends and undead. Basically all of the creature type effects are moved into the creature stat block.

The stat blocks are bigger, but you have to remember less about the game when using a stat block. This is friendlier to newer DMs, and IMO better for all DMs since the reduced cognitive load means better DMing.

For me, this is "six of one, half dozen of the other". Knowing that "all [type] have [whatever] trait" is easier than looking at a stat block to see if this particular [type] has [whatever] trait. At the same time, the stat block itself is an incredibly useful info-dump that took about 7 seconds to fall in love with the first time I ran a 5e game.

It's all about keywords. We learned the definition and mechanics of Immunity, Disadvantage, Restrained, etc., so it wouldn't be much of a leap to learn Undead, Beast, Construct, etc.

[Skrum]

I am also a fan of keywords, so I share your inclination. That said, it would probably change very little. Most creatures have all their stuff listed manually in their stat block already, so if you're a strictly by the monster manual DM, little to nothing would change.

But if you like homebrewing your own monsters, creature type traits would be very nice.

Personally, I'm most bugged by the playable races. Dhampir, reborn, and warforged in particular bug the heck out of me. What are they, besides "don't look too closely."

[KorvinStarmast]

(I recognize that this question fundamentally betrays a "why isn't 5e just the same as 3.5e?" premise. Let's set that aside for now.)

But that's your core issue.

Beyond the point on stat blocks doing what they are supposed to do, as noted above, another thing is that not having the "creature type do more work" prevents some player metagaming.

Just because on undead/demon/beast has this strength or weakness does not mean that they all do.
This in turn means that the DM does less work in tweaking and/or modifying monsters.
The stat block does all of the work.

Final answer: it is better for the DM, and the MM is a DM facing book.

[Kane0]

I can get behind creature type interacting with more things. Normally its the odd spell or class feature, plenty of room for it to toucb more things and it's already there built in to be used

[Psyren]

Does anybody know, or have any speculation, why that decision was made?

The big reason is that 5e wanted to avoid hidden/nested rules. A DM or player should be able to pick up a monster statblock or spell entry and know everything it does as a self-contained rules element. 3.5's system of tags and keywords and descriptors would have made (and did make) that impossible.

They still keyworded some elements (most notably conditions, e.g. Stunned and Blinded) but for the most part they succeeded at this goal, and arguably it contributed to 5e being the most accessible edition of D&D ever printed.

Would it break anything if I were inclined to reintroduce Type traits? Starting with, say, damage Immunities and Vulnerabilities -- off the top of my head, make Undead Resistant to Necrotic and Vulnerable to Radiant; make Fiends Vulnerable to Radiant; make Celestials Resistant to Radiant and maybe Vulnerable to Necrotic (I dunno, I haven't fully fleshed out the idea yet, just making sure whether there are or aren't reasons I shouldn't bother).

I mean, the big reason is that it might be a pain for your players and make things as fiddly as it does crunchy. But if they don't mind that then you wouldn't have anything to worry about either.

But there are indeed other pifalls:

Potential pitfall is that change specifically would turns Paladins into Undead- and Fiend-smiting god-machines... but aren't they kind of supposed to be, by the lore?

Keep in mind that paladins already get bonus damage vs fiends and undead, so you doing this would take the damage boost they get and boost it even further, likely unbalancing them vs. other classes in these kinds of encounters.

[KorvinStarmast]

and arguably it contributed to 5e being the most accessible edition of D&D ever printed.

While true, I doubt that matters to those who both loved 3.x and are still, 10 years after its introduction, unhappy that 5e isn't closer to 3.5 in various details.
(No, I won't bring up the never ending kvetching about the skill/ability check system).

[Thane of Fife]

Does anybody know, or have any speculation, why that decision was made?

It was almost certainly changed because it was a bad idea and poor design in the first place.

All Oozes and Vermin were Mindless;

Chickens aren't mindless. Why am I not allowed to imagine a spider that's as smart as a chicken?

Undead and Constructs didn't need to eat, breathe, or sleep;

So vampires don't need to eat or sleep? Ghouls don't need to eat? We can't imagine Frankenstein stitching together a flesh golem that needs to eat or breathe or sleep?

each Type had a specific hit die size and specific good/bad saves for all their racial HD, and so on.

And this was a bad idea. A fey knight and a fey wizard are both fey, but they obviously need to have different numbers of hit points (inasmuch as a melee character is more dependent on hit points than a wizard is). A bear and a panther are both animals, but the bear should be tough and the panther should be fast. A ghost and a skeleton are both undead, but they are conceptually almost as opposite as they could possibly be.

If you want to tie more things to creature types, that's fine and you can do that, but I would say that you should tie the type to the bare minimum amount of traits that you actually need to define the type. 3e ended up with weird stuff like Living Constructs and Deathless for the purpose of digging themselves out of the hole of overly constrained types.

[Psyren]

While true, I doubt that matters to those who both loved 3.x and are still, 10 years after its introduction, unhappy that 5e isn't closer to 3.5 in various details.
(No, I won't bring up the never ending kvetching about the skill/ability check system).

I'm not saying 3.5 fans aren't allowed to be unhappy, or that 5e design goals should matter to them. But the OP was specifically asking for reasons/speculation on why WotC made that design choice, so I answered their question.

[JonBeowulf]

<snip>
If you want to tie more things to creature types, that's fine and you can do that, but I would say that you should tie the type to the bare minimum amount of traits that you actually need to define the type. 3e ended up with weird stuff like Living Constructs and Deathless for the purpose of digging themselves out of the hole of overly constrained types.

This right here is the sweet spot. Don't follow the 80/20 rule and think it's gonna be good enough (<cough> 3.5 <cough>). It must be the minimum number of traits shared among ALL creatures of that type. Oozes are mindless... that makes sense. Beasts can be tamed and trained... actually, I kinda like that. Undead don't need to eat... not true. Undead don't need to sleep... Vampires do, so no. Undead don't need to breathe... probably okay.

If you go down this road, you must then resist the temptation to make a creature that violates the type 'cause it's cool and unexpected. It's neither. It's dumb and annoying.

[Duff]

If you want to tie more things to creature types, that's fine and you can do that, but I would say that you should tie the type to the bare minimum amount of traits that you actually need to define the type. 3e ended up with weird stuff like Living Constructs and Deathless for the purpose of digging themselves out of the hole of overly constrained types.

Also, do yourself and anyone who uses your work a favour. Put the "Category rules" with each relevant monster. EG, if all your Beasts have "Grumpy in the morning" then put that in the statblock for your new beast.
That could easily be a copy-paste where you have a section:
Beast - [all beast traits]

[kingcheesepants]

This right here is the sweet spot. Don't follow the 80/20 rule and think it's gonna be good enough (<cough> 3.5 <cough>). It must be the minimum number of traits shared among ALL creatures of that type. Oozes are mindless... that makes sense. Beasts can be tamed and trained... actually, I kinda like that. Undead don't need to eat... not true. Undead don't need to sleep... Vampires do, so no. Undead don't need to breathe... probably okay.

If you go down this road, you must then resist the temptation to make a creature that violates the type 'cause it's cool and unexpected. It's neither. It's dumb and annoying.

Oozes are actually a pretty good example of the very problem though. Despite being the creature type with the fewest number of creatures a good portion of them (the various types of Oblex, Plasmoids, Slithering Trackers, Sentient puddings etc) break the one rule you set out. So if you want to have creature type be more than just a tag that means certain spells don't work on them, you'll want to really boil it down, so much so that it may be sliding into generic uselessness again.

[Blatant Beast]

The common characteristic of Oozes are that they are amorphous, not that they are unintelligent.
Intelligent Gray Puddings, (or some type of psionic ooze that has reached sentience), have been around since 1e.

The 3e 'strait jacket' is something that should be avoided, and was avoided in 5e.

[JackPhoenix]

The common characteristic of Oozes are that they are amorphous, not that they are unintelligent.

And even that's not true, because the most iconic D&D ooze is the gelatinous cube, which may be squishy, but it's far from amorphous.

[JonBeowulf]

Oozes are actually a pretty good example of the very problem though. Despite being the creature type with the fewest number of creatures a good portion of them (the various types of Oblex, Plasmoids, Slithering Trackers, Sentient puddings etc) break the one rule you set out. So if you want to have creature type be more than just a tag that means certain spells don't work on them, you'll want to really boil it down, so much so that it may be sliding into generic uselessness again.

Easy fix... if you're going through the trouble of putting generic keywords on creature types, then don't use the creatures that violate the rule you've created. You're already deep into house rule territory so another step is not a big deal.

I'm neither for nor against the concept, my point is you gotta do it right.

[Blatant Beast]

And even that's not true, because the most iconic D&D ooze is the gelatinous cube, which may be squishy, but it's far from amorphous.

Which is a good example of why we do not need overarching characteristics to go with keywords.
We know a Gelatinous Cube is an an ooze, because the statblock indicates that it is.

Monster Design by it's nature, is one of the more exception heavy areas of rules design.
The utility of saying all Oozes must have the amorphous trait, and then making an exception for Gelatinous Cube, undercuts the idea of having overarching traits tied to a keyword in the first place.

Having general thematic similarities between creature keyword types seems reasonable, and I would argue that 5e does do this, but more than this is unnecessary in my opinion.

[stoutstien]

IMO a <type> should be general outlines on how they act rather than origins or physical descriptions.