Tales of Xillia, in hard mode fighting Jiao. Holy shit, it took me at least 2 hours to beat this bastard.
My damage did not go up 100 per attack and that's when he was incapacitated and he kept summoning minions that would start piling up. He hit incredibly hard and did the longest fucking combos. It was not until i started blocking every 5 seconds that I finally manage to take him down.