"You see nothing of note"

Breathing doesn’t guarantee that you can see something lol. Show me a breathing insect with its “chest” moving up and down. If you account for evolution then mimics who could best hide their breathing are also absolutely something that would happen. Plenty of mammals can hold their breath underwater a crazy amount of time. A mimic that could also position and shape its body would have no trouble hiding its breathing. They’re motionless and indistinguishable and you’re just going to have to deal with that. Bonus: the way to find them out would be to see if a character notices them looking out of place. Maybe it’s a contested stealth vs incestigation/perception role, or maybe the description of the room even has clues. There are absolutely other ways to “safely” discover them aside from breathing.

Because in my experience meta gaming like that is not an issue at 90% of all tables. And at the other 10% it's just that one guy that causes an issue about trying to meta game their character out of consequences. RPG Rules are not laws, so they are not written for the lowest common denominator, but for a group of well meaning, socially functioning, above room temperature IQ human persons with a base level of trust. Not every table preference has to be mentioned in the rules to be legitimate. At my table, there are no secret rolls or checks that a PC makes without a reasonably clear concept of what the consequences of success and failure are. So a list of default stats that your GM can check would be a waste of time and book keeping. If your GM likes to use mystical rolls with undefined consequences and the percussion of hidden dice to increase tension, more power to them. But to me that seems a waste of everybodies time.

What about the kind of evidence that leaves marks on the floor around where the mimic has been moving? Seems to me that's fair game

Of course it doesn't guarantee it. That's why you roll dice. Does evolution apply to aberations? And would evolution not grant the same benefit to every living being as well? Not to mention, co-evolution would lead to better mimic detection, surely. I don't see why I have to deal with your fiction over mine.

In Dark Souls, mimics breathe slowly. Like, 17 seconds per breath. It's tough to spot, but you can spot it if you're cautious. Since it's proven to catch people off guard, but CAN be spotted, I figure, why not use what works?

I brought up evolution as a way to explain the idea that even without magic it’s possible for there to not be any motion when a creature is breathing. There are also worlds where a mimic could be a normal animal, so that’s good there too. You, hilariously, are aaking if evolution even applies to aberations while being dead-set on them breathing, as if that isn’t a comically easy thing to hand-wave away if we’re saying the creature is a proper, built-for-purpose monster. The book says “motionless” and “indistinguishable”. Those words mean “_without_ motion” and “with _nothing_ to [visually] distinguish it from the object it is trying to imitate”. There is no breathing motion because then it would not be motionless and there is nothing to tell it apart. Both of those are ok in a game context because there other ways to discover the monster. We aren’t talking about your subjective opinion and your original comment was an “um actually” in relation to someone else’s so if you want to know why you’re having this conversation it’s because _you_ started it.

>which clearly says "a mimic in its altered form is nearly unrecognizable" Where does this "nearly" come from? Because my Monster Manual doesn't have that word in the mimic description...

I copy-pasted from the 2014 entry.

Note that a feature applying while motionless doesn't mean it is motionless. And based on the rules, no, there are no other ways to distinguish the monster if it is motionless. Look at the comment above mine. THAT was an um actually. OP described a perception check for a mimic, the comment I replied to said "um actually, there wouldn't be a perception check", and I replied with why there would be. Why are you making me the villain for defending the post?

I'm going ahead and hit "doubt" on that statement as I looked at my 2014 Monster Manual before writing my previous message and the word "nearly" is absent in that description.

I don't know what to tell you. I went to 5etools, looked at the 2014 lore, and directly copy-pasted that exact quote. You can check yourself. If I wrote it, I'd have spelt unrecognisable with an s instead of a z. Maybe it got errata'd at some point?

Ok, so I'm sorry about my previous tone, it seems that the mimic article, on 5etools and the SRD website, is the source of our confusion and disagreement: each time the description appears twice, first without the word "nearly" (under "False Appearance") then once with it. That 2nd description, under "Imitative Predators", does not appear in the Monster Manual. I could not check what D&D Beyond says because I do not have access to its contents.

Yeah, I think 5e tools uses the first ever printed version, while WotC reprint and edit the lore in the Monster Manual a LOT. D&D Beyond would probably be a third entry entirely. I'm glad we're on the same page now (or rather, we were on the same page, but the books were different).

Motionless and _indistinguishable_. Chests and crates don’t breathe and you’d be able to _distinguish_ the two very easily based on that. An _investigation_ check could work, or maybe a straight intelligence roll. Paying attention to the description of the room, too, and passive investigation is a real thing as well. I’ve already explained at least twice that you can use those ways to figure out that something isn’t where you left it or otherwise seems out of place. You can absolutely still find it using mechanisms that don’t require getting chomped. You’re just wrong. It’s fine, it happens, but the plain english is making it reeeeeally hard for me to understand how on earth you could be confused here.

Indistinguishable *if motionless*. If not motionless, distinguishable. You seem to be assuming that because it CAN be indistinguishable, it IS indistinguishable, and thus cannot be moving. Meanwhile, Dark Souls has mimics that breathe, and they work perfectly fine. Easy to get caught out, but definitely possible to spot if you're careful. Yes, you have explained twice how you can distinguish a creature that cannot be distinguished. And I've pointed out how paradoxical that is. Like, are you okay? Genuinely, I'm getting concerned for you.

Didn't know that, actually. How's their poison resistance? Can they hold their breath? Does D&D have spells that let you do things like deoxygenate a room?

Holy shit you’re dense. This isn’t Dark Souls and that’s a video game, not a table-top, theatre of the mind, RPG. If you can learn that the crate, _which is indistinguishable from any other crate_, has no reason to be where it is then you can perform further tests to expose whether or not it is a mimic. It will look exactly like a crate the whole time and that’s fine. It’s not a paradox, you’re just not very intelligent. You’re fifty-two cards short of a deck and making it everyone else’s problem.

They're immune to acid but not poison. They have a +2 CON mod, so they can hold their breath for 3 minutes, then have 2 rounds to breathe again or they die. It's rare for a room to be air-tight in D&D, but if it was, a simple "create bonfire" would do the job. Also, a mimic dying from smoke inhilation would be awesome.

No idea. Not even the most meta-gaming-est members of that party had a workaround.