there is one achievement in which u free nyx or become one with it or something like that that gives u the option of corrupting him and the guard you first meet if you start a game with it, aparently
I havent gotten it myself cuz the game sorta broke on my last save just after I saved it and it was my only save and I want to keep the achievements so I'm waiting for the next update lol
so idk how extensive it is, it's probs not that big a thing and will get expanded upon later