Swallowed creatures are considered Unseen Attackers. Yes or No?

Quote from MaximusArael020 >>

. . . we assume the reason you get advantage by being Unseen is "because with the attacker being unseen, the creature being attacked has a more limited ability to appropriately defend itself (either by dodging, holding up a shield, etc)."

This is true in your example with the Greater Invisibility scenario. The reason you get advantage is because the creature is limited in defending itself through dodging or holding up a shield because they cannot see the attack coming. Even if they know you are there, exactly where you are, they don't know if you are attacking high with an axe or low with a dagger. But this is not true for a creature within another creature.  

^ This is the part that I don't get about this argument?  Why is this not true for a creature within another creature?  If you cannot be seen, how does it know what you are doing with your axe or dagger?  It's the same thing.  Is the argument that the creature is a sitting duck anyway so it doesn't matter if he can see the attack?  In which case, perhaps the DM should be granting advantage for a whole different reason instead of the Unseen Attacker rule?  Why would that make any difference?  In the end, I guess this detail doesn't really matter -- we seem to agree on the end result.

Quote from MaximusArael020 >>

Again, strict reading of RAW the Adv and Disadv cancel and the swallowed creature attacks with straight rolls. However the OP seemed to be suggesting that the DM is hostile towards the players and "rules however they want", and seemed to imply that the DM was ruling this way as some kind of "gotcha" or bad-faith attempt to be overly antagonistic to the players. My point has been that it can reasonably be ruled either way.

 

Yes, I agree with all of this.  As long as it's clear that "it can reasonably be ruled either way" is referring to one way being RAW and the other way intentionally being not RAW.  How much that distinction actually matters to any given group will vary from group to group.

Quote from up2ng >>

Quote from MaximusArael020 >>

. . . we assume the reason you get advantage by being Unseen is "because with the attacker being unseen, the creature being attacked has a more limited ability to appropriately defend itself (either by dodging, holding up a shield, etc)."

This is true in your example with the Greater Invisibility scenario. The reason you get advantage is because the creature is limited in defending itself through dodging or holding up a shield because they cannot see the attack coming. Even if they know you are there, exactly where you are, they don't know if you are attacking high with an axe or low with a dagger. But this is not true for a creature within another creature.  

 

^ This is the part that I don't get about this argument?  Why is this not true for a creature within another creature?  If you cannot be seen, how does it know what you are doing with your axe or dagger?  It's the same thing.  Is the argument that the creature is a sitting duck anyway so it doesn't matter if he can see the attack?  In which case, perhaps the DM should be granting advantage for a whole different reason instead of the Unseen Attacker rule?  Why would that make any difference?  In the end, I guess this detail doesn't really matter -- we seem to agree on the end result.

 

 So, I actually addressed this in my first post:

"Now you might say "Yes, but the creature IS less likely to dodge your attack, because you are inside of it! How could it dodge or anticipate your attack!" and I get the argument, however that really wouldn't come from being "unseen". That isn't the case that the target has a limited ability to avoid your attack due to not knowing where the attack is coming from or seeing the attack, but much more like an attack made against a Restrained creature. You get advantage on a restrained creature because they physically cannot (or have limited ability to) anticipate and/or move out of the way/block the attack. That is much more similar to what is actually going on with attacking from inside of a creature."

While D&D is not a real-world physics simulator, I think as a DM it is important to understand why a rule exists, how it is meant to work in the world, and under what circumstances it is meant to come into play. Because as we all know, with players doing everything they can to bend the reality of the world to their will, much of our time as a DM when it comes to rules interactions is interpreting edge cases and figuring out how opposing or vague rules might apply in a given situation. 

In the case of Unseen Attackers, while it isn't spelled out in the rulebook, I have a vision for why the rule works as it does (which I explained in the Deer example and also in that "because with the attacker being unseen, the creature being attacked has a more limited ability to appropriately defend itself (either by dodging, holding up a shield, etc)." This is the framework I use to decide when to apply the Unseen Attackers rule. The basic premise being that the target is less able to defend itself how it normally would (dodging, holding up a shield, etc) because it cannot visually perceive the incoming attack. That's why I would not apply Unseen Attackers to the creature inside the stomach. It wouldn't matter if the creature was invisible or not, the reasoning behind the advantage given for unseen attackers doesn't logically flow with the situation. The target is not more likely to be struck because of its inability to move out of the way of or anticipate the attack.

That's why I said I would still understand granting advantage to the swallowed creature based on the rules for a Restrained creature (though the swallower doesn't have that condition) because it makes sense for a target that is not physically able to move out of the way.

Though the ending might be the same, the way we get there is different. And because D&D is not just this one question, asked by the OP, it is important, especially as a DM, for me to understand the pathway to the ruling and to have them make sense to the players.

Example: a creature is both bound AND has a blindfold over their eyes. They are chained to the ground and cannot move, thus having the Restrained and Blinded conditions. Another creature attacks that bound creature. The attacking creature has Advantage on the attack, obviously. But why? In this case is it from being Unseen? The fact that it cannot anticipate the movement and thus dodge out of the way? Eh, you could maybe argue that, but for me it is the fact that they are bound, chained down, physically incapable of moving out of the way of the attack. So as a DM, that's how I narrate it. 

I think in cases of the OP's question it is important to not only give the RAW answer (which I did), but also explore the bigger context around it. D&D is not played in a vacuum of "absolute textual rule truth". So to just say "RAW you're right" misses on a deeper understanding of things. For instance, like I said previously, OP seemed to be suggesting that this ruling was part of a pattern of hostile, player-antagonistic rulings by the DM. My suggestion being that, while RAW it would be a straight roll, it was fully defensible and logical how the DM ruled, if outside the scope of a sterile reading of the rules. 

So yes, from each of us the end result is the same. I mostly just like to provide myself a logical (to me) framework with which to judge how rules are intended to work and when they might apply, which perhaps for others seeing how I view the intent of the rule to work would be beneficial for their tables or to other DMs who might have a similar mindset. Neither side is wrong and both viewpoints have value, and the fact that different tables play things out differently is part of what makes D&D such an amazing game to play.