Wright on 05 June 2016
I wouldn't be able to name a single one as the "hardest". The first one that came to my mind when I read the title, however, is Metal Gear Rising's final boss. Considering how that game gets progressively easy as you keep going, the endgame boss was such an unbeatable foe. It literally forces you to reassimilate your gameplay style, all in one combat, to find a chance to win.
