"You shall meet enemies three, but none more dangerous than yourself in your full glory. They are shades of evil, of good and neutrality.."

This quote. When I heard it from Deionarra I always figured it was suppose to mean something special but at the end I'm not sure what characters were suppose to represent them. I assume the game developers had something in mind but maybe it's up to speculation as well.

I read somewhere that the good one was Trias, the neutral one was Ravel and the evil one was Fhjull.

My own interpretation is this: the good one was Trias, the neutral one was Lady of Pain and the evil one was Ravel.

I assume here that since Trias was a deva or celestial they are suppose to represent the opposite of the fiends. The good in people and all that. Lady of Pain, the neutral force that doesn't bother with good or evil but only the state of Sigil. Ravel, well..somewhere in the game, I think multiple people mentioned she was an enigma even to the Night Hags who BTW were evil and cunning, Ravel was just worse.

While I like the character Fhjull he was such a small part in the game, I had hoped for me interaction with him (with difference outcomes of course) :)

Maybe she was talking about the 3 previous incarnations you meet near the end.

That's a possibility.

The three incarnations met in the Fortress of Regrets was also what I took that line to refer to. I note the phrasing "yourself in your full glory" rather than just "yourself", and take the view that this was used as a form of subtle riddle rather than just to be verbose. Also, the use of "shades" is probably a play on words, both simultaneously using it to mean "gradations" (as while the incarnations certainly do each lean towards good, evil, or neutral, they are also all more complex than simply being stereotypical good, evil, or neutral beings), but also drawing on "shade" being a synonym for a ghost or spirit of one who died, which is a more literal description of the three incarnations.

The writers for PST were very good at what they did, and this kind of subtle layering of meaning would definitely fit with their overall style for the game.

I always assumed this was meant to be interpreted on multiple levels and to further reference The Rule of Three.

Three incarnations, three godlike beings (Trias, Lady of Pain, Fhjull), three ideologies (Lady of Pain's hatred of those who worship her, Trias's strange perspective on good, and Ravel's complete indifference and interest in the puzzle of The Nameless One), probably a few more threes I can't remember off the top of my head.

I always figured it was your split selves too, since that's where Deionarra is hanging out these days and what she tells you is you'll face four enemies that are a genuine risk to you. The shades (shards) of your former self and an aspect equal to your former glory (TTO).