Are you facing the White Cyclops alone? You don't have to have any companion, nor do you have to wear Violet. And also, you have to defeat the other black cyclops: only the white cyclops must remain.
I'm facing the white cyclopus alone and I kill the other two cyclopus, I don't use any glace/violet armor, before going to fight I prepare 1 anti-sleep potion, 1 anti-bruise potion, 1 magic potion, 1 regeneration potion, all of these at 40%, but I just leave these potions to fight the final boss (which in this case never appears)
