The Koshchey must be fought in a confined space and has the ability to incapacitate even a well-prepared Geralt; for me, this has to be the toughest boss fight.The Kikimore Queen is almost unbeatable if your Geralt tries to fight her directly, but the game gives good hints as to how to dispose of her without confronting her.You could argue that the Beast is an unfair fight, because the game mechanics give Geralt no good opportunity to prepare, but if Geralt hasn't learned that hellhounds fall quickly to Aard, he's not as smart as he looks.Roland Bleinheim should be in the poll as the toughest human opponent, not because he is so tough himself but because of the army he brings to the dance.