AoE Blindness Adv/Dis negation?

Actually in 5.5e it is reasonable to assume that Total Cover does, in fact, block the Darkness spell. Per the rules for Area of Effects: "If all straight lines extending from the point of origin to a location in the area of effect are blocked, that location isn’t included in the area of effect. To block a line, an obstruction must provide Total Cover."

The 5e version of Darkness included the line "spreads around corners," but this was removed from the 5.5e version of Darkness. The word "spreads" is not really enough to override the rule of how AoE's, well, spread.
Many spells had that terminology - "spreads around corners" - in 5e, and it was removed from them in 5.5e (just look at 5e Fireball vs 5.5e Fireball)
I believe this was done intentionally to improve the benefits of being in Cover, as Total Cover not blocking spell effects made trying to be behind it pretty lackluster and pointless in 5e.

Quote from Squirrelloid >>

Quote from Jaysburn >>

While the rules for sneaking in this game are quite lackluster, if you're allowing being in Darkness/Fog or being Invisible (etc.) to automatically hide where a creature is (what space they're in), then you're essentially causing any such feature to automatically include the Hide action, and that's quite OP. 

If you're not, then the invisibility spell is pointless, and the hide action doesn't do anything (because all the hide action does is make you invisible).  

So yes, being unseen is in fact identical to the hide action, RAW.  (The only difference is in the conditions to end that 'invisibility').

I can't imagine playing in a game where you still had perfect knowledge of where everybody was even when you couldn't see them.  I doubt anyone actually plays that way in practice.  Do you tell your players what's behind a closed door, down to their identity and position in the room beyond?  I don't think so.  Yet there's no real difference between that closed door and a fog cloud.

 
This has also been argued to death all over these forums and elsewhere, so I'm reticent to get into it again.. but heck, why not.

The Hide action does do more than simply giving you the Invisible condition. In fact, they added a (fairly weak) errata to the Hide action which cannot be seen in the tooltip popup, but can be viewed in the glossary.
The Hide action does indeed make you Invisible (which I personally think is very stupid), but it also allows you to "try to conceal" yourself, to "become hidden," and - most importantly - make a Stealth check, which in turn allows you to "escape notice". In fact, the Hide action and the Stealth skill are the only places in the rules where terms that imply going unnoticed ("conceal yourself", "become hidden", "escape notice") exist, and the Hide action is the only way that a player can actively choose to make a Stealth check.

If simply gaining the Invisible condition were enough to make you hidden and allow you to escape notice, it would say so, but it does not. If the Invisibility spell was intended to do those things, it would say so, but it does not. Conditions do what they say they do, and no more; the Invisible condition doesn't allow you to conceal your presence and go unnoticed any more than the Poisoned condition does. It doesn't even allow you to make a Stealth check; you need to Hide for that. 

This does not make the Invisibility spell pointless by any means, as you still gain the potent benefits of the Invisible condition through it. It can additionally allow you to go out into the open when you are under the effects of the Hide action, which would normally cause you to "stop being hidden." 

As to your final question, simply put, the game plays differently in combat - in initiative - than it does outside of it. 

Quote from up2ng >>

When it comes to Darkness, a creature is blinded only when they try to see something that is within that Darkness. 

 Correction: the way darkness works is heavily disputed.

Quote from MaximusArael020 >>

Quote from Squirrelloid >>

2. Darkness spell description:

"For the duration, magical Darkness spreads from a point within range and fills a 15-foot-radius Sphere. Darkvision can't see through it, and nonmagical light can't illuminate it.

Alternatively, you cast the spell on an object that isn't being worn or carried, causing the Darkness to fill a 15-foot Emanation originating from that object. Covering that object with something opaque, such as a bowl or helm, blocks the Darkness.

If any of this spell's area overlaps with an area of Bright Light or Dim Light created by a spell of level 2 or lower, that other spell is dispelled."

Couple things to note:

--magical Darkness spreads.  It's a 'physical' thing (in the same sense light is a physical thing) that is present, not just an absence of light. 

--It fills the 15' radius sphere. It doesn't just cover objects in it, the whole space is filled with magical Darkness, not as an absence, but as a presence.  And to constrain it, you have to completely encase it in a physical object that blocks the darkness from radiating outwards.

--Nonmagical light cannot illuminate it. Not 'can't illuminate objects in it', can't illuminate "it", the magical Darkness.  So the whole space cannot be illuminated by light, including the air.  And that also means light cannot pass through it, because to pass through it would be to illuminate the space it passes through. 

--Darkvision "can't see through it", where "it" is again the magical Darkness.  Not can't see objects in it.  Can't see through it.

Pure RAW, you can't see through magical Darkness, whether inside it or outside it.  That's completely unambiguous if you actually read the spell description.

 

 

I feel like you are putting a lot of weight on words that hold no real technical/rules meaning, and are mostly mean for flavor. 

The Darkness spell creates "magical" Darkness, which behaves exactly the same as mundane Darkness except for the things specifically called out in the spell. Those are that it cannot be illuminated by any light source unless that light is created by a sufficiently powerful spell, and that Darkvision cannot see "through" it. Those are the ONLY differences between it and mundane Darkness.

It makes sense to say that it "spreads" from a point, because if it merely emanated from a point then the Darkness would be blocked by things that provide total cover. So if you were behind a low wall 5 feet from the object that the Darkness spell was cast on, you wouldn't be in Darkness at all because you were behind cover. The "spreads" means that it goes around things that might normally provide cover. That's all. It doesn't turn the Darkness into a "physical thing" that literally fills the space. The rules don't say that at all. It "spreads" because otherwise you could take cover from it. 

Your other points where you say "It doesn't say light cannot illuminate objects in it, it says it cannot illuminate it, the Darkness" is reading too much into what the text says. For one, it doesn't say "objects", because it would then have to say "objects and creatures". But if it only said "objects and creatures", some people might think "well, magical light lets you see things in the darkness, but not through it because the air isn't an object or creature". So instead the rules use the very basic term of illuminating "it", the Darkness, not because the Darkness is some physical entity filling the space to block light, but because it is the simplest and most likely to be understood for the average English speaker as "oh, the light illuminates the whole space and everything in it, like normal." It's just the most concise way to say what magical light of a certain level will do, instead of having to say "Light of 3rd level or higher will block the Darkness in the radius of illumination, making visible objects, creatures, and the unfilled spaces in between objects and creatures."

This is the same for the "Darkvision cannot see through it" part. It doesn't specify "Darkvision cannot see Objects in the area of magical Darkness" because again, it would have to include Creatures as well, and would be overly specified. Just saying "cannot see through it" is common enough language that most people understand what it's saying. "Oh, even if I have Darkvision, it basically doesn't work here."

In fact, we KNOW that light must still be able to pass through the magical Darkness to a certain extent, because Truesight says "Darkness. You can see in normal and magical Darkness." The spell Darkness does not block Truesight, and if Darkness created a physical entity that literally blocked all light from entering it, then Truesight wouldn't work. Notice that Truesight does NOT work with something like Fog Cloud (which DOES actually create a physical sight-blocking thing in the space: fog). 

 

 So your argument is that we should ignore the words they actually chose to describe how magical Darkness operates?  If you're not following the words, you're not using RAW.

Yes, I put a lot of weight on the words they chose to describe the spell. Those words have obvious mechanical implications and are easily interpreted 'technically', even if not predefined.  And I'm using exactly what the spell description says to understand how it differs from regular darkness.  Regular darkness does not 'spread'. Light can illuminate it, and to the extent you can see through regular darkness, it is because light is illuminating it.  

DND is not a computer RPG.  We can use words to describe things which don't have predefined technical meaning and aren't required to have things function in a rigid code framework.

And no, something spreading has to be a something, because something has to be doing the spreading.  Regular darkness is not a something.  (And evocation spells create energy; Darkness is not an illusion spell.  Spell school means something).

Expecting Darkness to explicitly specify objects and creatures is not overly specified.  That would be proper technical language if and only if your reading is correct.  That it does not say that is evidence against your interpretation.  (And indeed, literally every word choice and description in the spell supports my reading.  You have to literally rewrite the spell in its entirety to get your reading).

Truesight foils regular and magical Darkness because it says it does.  It's magic.  It doesn't require light to work.  You can't conclude anything about Darkness from Truesight working.

And if you insist on only implementing words that have a defined 'technical' meaning, then you can see through a fog cloud, too.  It just says the area is heavily obscured, which if you're going to read that to mean you can only not see things in its area like you want to for darkness, then you can see things on the other side of the fog cloud without issue.  (And we're back to indescribable again).  (Similarly, an area of heavy foliage only heavily obscures what's in it.  You can see through the physical foliage just fine to see what's behind it, no matter how thick it is, if you're going to be that limiting in your reading).

Explain the thought experiment scenario 2 in #3.  How do you even describe what is going on if your interpretation is correct?

Oh boy, here we go again... Yep! While not an actual condition, "hidden" is a game state (as per the definition of a state machine) that you gain after succeeding on a DC 15 Stealth Check as part of the Hide Action.
What this game state entails exactly is what's heavily debated because the designers never bothered to formalize it clearly and explicitly.
But what makes the most sense imo is that enemies simply can't perceive you in any way unless they have a special sense like Truesight or if you do one of the things that are explicitly stated in the Hide action (you make a sound louder than a whisper, an enemy finds you, you make an attack roll, or you cast a spell with a Verbal component).
Some people read "an enemy finds" so broadly that they completely ignore the hidden state and the invisible condition and the need for a Perception check and say that they find you if you're near them or somewhere within their line of sight.
A lot of people here won't admit it, but the main problem is balance: if you read Stealth rules honestly, it's too strong (especially for a Rogue), and if you read them conservatively, it's completely useless.
Whenever I want to play a Stealt-based character, I always make sure to dip in Ranger and start with or quickly grab a Nature's Mantle.
This item ensure that you can play Stealth effectively even if your DM has a very restrictive reading of Stealth rules.

Quote from Jaysburn >>

Quote from Squirrelloid >>

Quote from Jaysburn >>

While the rules for sneaking in this game are quite lackluster, if you're allowing being in Darkness/Fog or being Invisible (etc.) to automatically hide where a creature is (what space they're in), then you're essentially causing any such feature to automatically include the Hide action, and that's quite OP. 

If you're not, then the invisibility spell is pointless, and the hide action doesn't do anything (because all the hide action does is make you invisible).  

So yes, being unseen is in fact identical to the hide action, RAW.  (The only difference is in the conditions to end that 'invisibility').

I can't imagine playing in a game where you still had perfect knowledge of where everybody was even when you couldn't see them.  I doubt anyone actually plays that way in practice.  Do you tell your players what's behind a closed door, down to their identity and position in the room beyond?  I don't think so.  Yet there's no real difference between that closed door and a fog cloud.

 
This has also been argued to death all over these forums and elsewhere, so I'm reticent to get into it again.. but heck, why not.

The Hide action does do more than simply giving you the Invisible condition. In fact, they added a (fairly weak) errata to the Hide action which cannot be seen in the tooltip popup, but can be viewed in the glossary.
The Hide action does indeed make you Invisible (which I personally think is very stupid), but it also allows you to "try to conceal" yourself, to "become hidden," and - most importantly - make a Stealth check, which in turn allows you to "escape notice". In fact, the Hide action and the Stealth skill are the only places in the rules where terms that imply going unnoticed ("conceal yourself", "become hidden", "escape notice") exist, and the Hide action is the only way that a player can actively choose to make a Stealth check.

If simply gaining the Invisible condition were enough to make you hidden and allow you to escape notice, it would say so, but it does not. If the Invisibility spell was intended to do those things, it would say so, but it does not. Conditions do what they say they do, and no more; the Invisible condition doesn't allow you to conceal your presence and go unnoticed any more than the Poisoned condition does. It doesn't even allow you to make a Stealth check; you need to Hide for that. 

This does not make the Invisibility spell pointless by any means, as you still gain the potent benefits of the Invisible condition through it. It can additionally allow you to go out into the open when you are under the effects of the Hide action, which would normally cause you to "stop being hidden." 

As to your final question, simply put, the game plays differently in combat - in initiative - than it does outside of it. 

"With the Hide action, you try to hide yourself. To do so, you must succeed on a DC 15 Dexterity (Stealth) check while you’re Heavily Obscured or behind Three-Quarters Cover or Total Cover, and you must be out of any enemy’s line of sight; if you can see a creature, you can discern whether it can see you. On a successful check, you have the Invisible condition while hidden. Make note of your check’s total, which is the DC for a creature to find you with a Wisdom (Perception) check. You stop being hidden immediately after any of the following occurs: you make a sound louder than a whisper, an enemy finds you, you make an attack roll, or you cast a spell with a Verbal component." SRD 5.2.1 p183.

As far as I can tell, that's the most recent systems document.  Nothing about Hide giving anything but Invisible.  (And no rules glossary in it).  I'm sorry, if they want to change the rules, they need to actually change the rules and publish a real errata.  The rules glossary is not the rules.

But you do not stop being Hidden when you go out into the open.  That is not an ending condition for Hide's Invisibility.  You have to be found, which is only defined as 'a successful perception check'.  You could hide, walk up to the guard, and dance a jig in front of them, and they'd see nothing so long as they couldn't beat your stealth roll.  Not only does hide nowhere require you to stay behind cover, it would be completely non-functional if it did.  (The only place i can recall which requires a hiding creature to end behind cover is the Thief Rogue's supreme sneak, which lets you stay invisible after making an attack - something that would normally break the invisibility - and it only requires you to be behind cover to achieve that specific effect at the end of your turn, not continuously).  Any language about being discovered when you were in plain sight have been stripped from the 2024 rules, and quite intentionally.

And no, initiative is only different from not initiative because it allows for precise sequencing of actions.  Rounds still tick normally out of combat.  That we leave initiative when we don't need it is a matter of convenience (because precise sequencing doesn't matter), not a difference in world physics.  Are you literally advocating that a pea soup fog (magical or not) denies you the ability to precisely locate other creatures out of combat, but if you shoot an arrow or swing your sword into the fog, suddenly you know where everyone is?  I don't feel like that's a position that needs to be taken seriously.