I haven't completed the game yet but the two toughest bosses for me so far were Koloktos (which I had a feeling it would be from seeing the pictures and reading the long description of how to defeat him in the strategy guide; I found there was very little room to run to escape from some of his attacks, I often got blindsided, especially the sword throws), but using one of his swords to chop his arms and legs off was great fun. Also Scervo was a nightmare because shield bashing doesn't really protect you when he thrusts his sabre into you, plus that attack takes two whole hearts off your health meter. Out of the two it was Scervo who gave me a couple of Game Overs usually because I never got a chance to drink a potion in time when I was low on health (maybe the Guardian Potion would be useful in future lol), whereas Koloktos took me about 10 minutes to defeat without getting a Game Over.