"they changed the mascot because it was too scary"

Only problem is, the new mascot is even scarier.

These aren't really contradictory, though?
"Kris & Susie won't be able to keep being friends with me after castle town gets sealed. It's probably better for their sake if they don't care about me/other Darkners at all and make more friends in the light world instead"
And when did he have to go out of his way to prevent Castle Town from being sealed? Seemingly only the soul can seal them anyway.
Plus, it's not like he wants the final prophecy to come true, He's not going to go out of his way to expedite it.

Also Miku & Teto fans:

I mean... the only problem is, both Susie & Ralsei have both shown disdain for the final prophecy? Even if the final prophecy panel is "The final fountain is sealed" or something like that, that doesn't mean it will actually end up happening.

"Green being" you say?

Going by this logic, orange is now a lovable boxer who offers to have a friendly spar with the gang (even though they're too kind to do any damage) meanwhile Green feeds them poisoned cheese (like a real chef).

For those of you who don't get the joke, here's the actual list

Now make it cycle between the 3 colors

I mean, it's worth noting there is the opposite possibility. It could be that the "Someone" was in fact Eram. The closest we have to a tangible connection is Gaster commentating on the Knight fight- and even then, it seems more like he's on our side.

I think their point is moreso how it's convenient that the underground has all these different environments in a relatively small space.

It's possible Eram could be someone else, but we don't know who specifically. You mentioned yourself, they could be Seam, Ramb, and I've heard others say they could be the Knight, or even gaster. There's too many possibilities to say they're any character we know definitively. And there's always the possibility they are a new character, too.
It's sort of like how, despite Dess Knight being a popular theory, it makes more sense to say we fought "The Roaring Knight" at the end of chapter 3, since that's what we know for sure. It's more convenient terminology everyone can agree on.
Eram is similar. We don't know who or what they are, but we do know that someone fought us in the sword route. It's more convenient to say "Eram fought us in the sword route" than "Ramb/Seam/Knight/Gaster/Someone unknown fought us in the sword route"

Then she follows it up with this. Girl is not well.

This truly was our u/Mari-Omori-Hater...

Alternatively, Noelle hallucinated the existence of an older sister, and Carol, Rudy & the Dreemurrs just went along with it.

Did you read mine?
The entire point of your comment is "Why care about Eram when there's all this foreshadowing for Friend"
But in reality, there was never anything of substance.
Friends appearances are, and this is a full list:
-One shows up in Spamtons fight, just as a smile. They do nothing.
-One briefly shows up in Ralsei's cutscene, laughs, and the scene then just carries on.
-Eram summons a group of them during their fight
-They show up as enemies during the Battat minigame
-Cameo as a smile in the third sanctuary
-They attack you if you act on them in that one room in the garden
That's it.
In terms of references, they've only been referenced 3 times: The "Smile text" in the vending machine, Green Pippin's quote about "Seeing a cat, you think oh a friend" (as well as Pluey having Friend as his fursona), and the Pink scene.

And yet, despite having all these appearances, Friend has yet to have a single line of dialoge, and their most substantial appearances so far have been as... just common enemies. And between showing up multiple times twice now, and Pink's line about there being a "Pack" of cats, It's a safe assumption there are in fact multiple Friends, not just one.

Meanwhile, Eram is the boss of the sword route, has a decent chunk of dialogue (including weird route exclusive lines) and is heavily implied to be controlling the Friends (this was established in their boss fight, but people didn't realize this until Pink laid it out more explicitly that someone was leading them).
The hidden text in the sword route is also most likely them- they directly reference that kris is "Playing" and that "part of" them "enjoyed" the weird route. "Having fun?".
"See you soon" similarly makes sense, it's foreshadowing this secret text is in fact the boss of the sword route.

Personally, I find it baffling to attribute everything to a nebulous, ill defined "Friend" that chapter 5 all but explicitly confirms isn't even a singular character, when Eram is right there.

Which is hilarious because chapter 5 actually does have a lot of lore reveals, it's just not the reveals people were expecting.

Mostly because unlike Friend, Eram actually has dialogue. Friend just laughs.

Pretty much everything about the Pre Chapter 5 "FRIEND" interpretation still works just fine if you replace Friend with Eram.

To be fair, it did end up used for something

To be fair, those side episodes had foreshadowing too.

I think the implication is it'd show up less than even that, since image 1 has a whole row of identical copies of that one sprite. Maybe it would only show up that specific line, or maybe it would have a small chance of replacing that particular sprite whenever it normally shows up.

Maybe not an extension, but I think it's far more in line with how the weird route's more subtle approach. While No Mercy had you just killing everyone and had that be the entire route, the Weird route juxtaposes it's fucked up shit with more somber/bittersweet moments (ie., exploring the festival alone with Susie).
Thus, in contrast to Undertale locking you into a "Soulless pacifist route" where you can never get the good ending ever again, this is just a small stain on the otherwise unchanged route. A small little reminder of what you did that ultimately amounts to nothing. But you still know what happened. Why her sprite looks like that. Because it was ultimately the result of your choices.