>>21132
>First red herring: why would you ever make such a deal
Ten minutes into the title screen after a genocide run and the first fallen human appears. What he mentions is, however, fairly scary: he will offer you to recreate the world so you can keep playing… if you sell your soul. Who in their right mind would do such a thing, you ask? Well, apparently many people.
What I was trying to get at is, everything about the first fallen human seems too weird. It is almost as if he was supposed to be the human incarnation of the Devil, in game terms. He wants to destroy the world, he is evil (duh), and even asks naive humans to give their souls in exchange for something that's far of being worth an eternity of suffering.
We have to go outside of the underworld to understand the purpose of this. More specifically, Twitter may be a good place to start.
Toby Fox suggested in his feed that you should name the player character after you. That is, if your real name is John, you should introduce John. Most people shrugged it off as Radiation just wanting you to self-insert, but is it all there is to it? After all, it seems like he specifically encouraged this to make the player get engaged in some sort of twist (namely, "no John, you are the demons!"), but this twist doesn't make sense. If the first fallen human is indeed the player, why the fuck would you sell your soul to yourself? It seems ridiculous. Not to mention that this pretty much implies that the player is always evil, since when it is being a pacifist, it is actually Frisk doing the good acts.
To make it scarier, it seems that the file that signals if you have sold your soul is the only special marking file that gets uploaded to Steam Cloud if you are using the Steam version. As such, it is somewhat difficult to get rid of it, and that is if it ever gets deleted instead of just "disabled" in Valve's servers. That may mean, the file will only get deleted when Valve goes bankrupt and scraps the servers or decides to free up some space (the first one being more likely, since companies only delete user data if they are fearing a lawsuit), and we never know when that could happen. Fuck, it may be one of those companies that will outlive you.
Could it be that Toby wanted you to associate your name with said contract with the first fallen human?
>Second red herring: goats
Toriel, Asgore and Asriel are all, although to different degrees, somewhat evil. Asgore is the king of the underworld, and he is on a quest to steal human souls; Toriel,even being the most benevolent of the three, still seems to think that sacrificing six humans is a great idea, thus showing some Machiavellian moral axioms; and of course, Asriel has a demonic appearance, wants to steal souls for power, and is soulless himself.
May I remind you who is identified with a goat, and is on a permanent quest to acquire souls? Yeah, you guessed it.
>Third red herring: monsters = demons?
The underworld may be a metaphor of hell. Fuck, it is possible that Frisk died on his fall to the Ruins and the whole game is about escaping hell. Think about it: most of the monsters aren't exactly nice (although you may argue that they simply have a different set of morals, guided by something else than right or wrong), they were banished into the underworld (where Hell is traditionally located), they are magical beings and not material, they want to escape that place and flood the human realm…
>Fourth red herring: W. D. Gaster
Not much is known about this character, other than it seems to be Undertale's Uboa: a really obscure easter egg consisting of a white face that pops up only if you perform some really specific tasks. In Yume Nikki, it was as "simple" as flipping a light switch over and over, but here it requires messing with your save files or just decompiling the game and looking at the source.
We learn it is some sort of being that is omnipresent in the fabric of the game's reality, but can't interact with the world so he is forever stuck as a permanent observer of the universe. All we know about him is that he used to talk in WingDings ("talking in hands", W. D., some audiologs in WingDings…). that he used to work as a scientist, and that he was the person who made The Core, which is the structure powering the entirety of the power grid of the underworld (which may be a meta-joke trying to relate The Core to the game engine and files, considering it's the only place where Gaster has an actual presence). One character tries to warn you about him in a somewhat cryptic manner, but why?
The answer may be inside the game's source, where W. D. Gaster's ID is 666, despite the fact that the highest number before that one is 100.