Nope, she has 3 H-animations and all you have to do is be stripped but then escape from her mindfuck hold. You might be right that it's based on lust for which of the other two animations she uses though. Sometimes she'll just try to mindfuck you again but usually she'll move on to the other two H-attacks.
I haven't seen that one yet, interesting. I figure it'll be a pain in the ass to achieve since I've barely broken out of her hold, and when I do, I'm already at max lust, she gets a free turn, then the fight's over. Also, when you say being mindfucked, does it mean she performs another move when she binds you instead of just using her tentacles?
Whats this about some people having a stone from the new mind flayer and calling her? I both defeated and lost to her, only got a Lust potion as drop.
Also my completion says 100%
When you fight Elith and win, you'll get Cephrina's Eye. It's an item that lets you interact with her in most safe locations, and her interactions are the same as if you went to the aqueducts instead. I think you only fought Cephrina, the mind flayer itself. She gives out Lustians, used for lust potions
Fair warning though, if you plan on fighting her and deliberately choose to lose, the game will softlock since she won't teleport you to Elith, nor will it trigger any other special scene. It also screws over some scripting since when you fight her, she also tries to use that same eye, which, naturally, doesn't work. Not sure if it will have an effect like how Nel takes over for you and auto fights on random places for experience/relationship purposes.
Also, did anyone notice that on the Equip menu, it also displays the fact that Cephrina also scrambled something in Celica's mind? Wonder if that's gonna turn up as a gameplay feature or story element...