No. No. This is not tin foil hatty. You know why? The tomb to the Emerald Knights is where they hid the truth of what caused Red Crossing. An elven-human skirmish. It's clear that both sides are to blame and I don't want to open that hole can of worms into a moral discussion at present (or ever because I see both sides as deeply flawed and refuse to side with either). But those elves within the story itself were deeply paranoid, angry, and seeking to villanize the humans just as much as the humans were them.
If these Emerald Knights were so desperate for revenge against the humans who led them to betray one of their own without realizing it - I can't imagine how they WOULDN'T turn to worship of the Forgotten Ones if that's a thing in lore that some elves do.
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I'm less worried about the fact that various groups of elves were worshiping one of the Forgotten Ones, and more worried that doing so seems to have actually worked, in the case linked in the wiki. As in, the elves who sacrificed to this particular god actually got power out of the deal.
That... really shouldn't happen, given what we think we know about who was sealed away at the time, and who was free to interact with mortals. It's entirely possible the power was granted by a completely unrelated but opportunistic demon/spirit who got something else out of the deal. But- and BEWARE this is deep into tin foil hat territory- I'm getting a little worried that Solas may not have direct control over Falon'Din anymore.
It's possible that he's recovered his original body, and the small scar on his forehead is a wound from the first failed rebellion of Arlathan: specifically, where he was "bloodied in his own temple". A small lyrium brand, part of the usual punishment for treason, if we can draw from the limited evidence of Andruil's ToM mosaic. No doubt this was intended to function much like Chantry Tranquility, severing him from his fade shadow and rendering him a non-threat to the Pantheon.
The interesting part, of course, being that Dirthamen/Falon'Din's fade-side presence (his "self" or Will) had been strengthened to the point where the two halves of his being were able to function independently. This split hobbled Solas-as-Dirthamen, but would have had little effect on Falon'Din. Dirthamen thus remained trapped in Dread Wolf form until his restoration as Fen'Harel- but when that occurred, what if this mini-Tranquility was not entirely reversed when he was restored? What if his current limited powers and general temperament come from an attempted restoration by a Spirit of Wisdom, similar to the Seeker rite but leaving his two sides: his physical self and his soul, as separate entities? Judging from historical events, the two seem to have been working largely in concert since then... but these words from Mythal in DA2 made me pause.
"Regret is something I know well. Take care not to cling to it, to hold it so close that it poisons your soul.”
This... honestly worries me. We know our actions and emotions in the real world twist the fade accordingly. It suggests Solas as a parallel to Dorian Gray: his current serenity and calm a mask for the tremendous damage his pain and regret are having on his soul, Falon'Din.
"There are few regrets sharper than watching fools squander what you sacrificed to achieve." -Solas
This, then, if you want to make a tinfoil hat big enough to use as a tent, could represent the creature we see here. It may be a representation of Falon'Din as one of the Forgotten Ones, semi-stricken from the Pantheon while Dirthamen was trapped in the Void, giving rise to a cult within Elvhen society during that time who would have only cared that he was a God still able to answer prayer with power, and who persisted in this fashion even after Dirthamen / Falon'Din were restored to the Pantheon as Fen'Harel.
It's a tremendously scary thought, and a bizarre kind of madness- to be separate from your own twisted soul. Still linked, but unable to reconnect directly. If we're wiling to entertain the basic idea, we must also to be willing to entertain the possibility that Falon'Din's objectives may have diverged significantly from Solas' in the time since the Andrastean rebellion. He may seek a final end to the Dance. One that cares little for the cost to the mortal, physical world.
*takes her tinfoil hat off, throws it out the window*
BRING ON THE SMUT.