I platinumized the game so I eventually learned to beat them all with relative ease because the game otherwise just demolishes you but I would say the toughest time with the Secret Final Boss from the whole Past Pseudo Time Travelling sub arc. I cannot tell you who that was because I do not know if it is gonna be a spoiler for you. During my first playthrough basically all was hard for me. Even the first few enemies or Masataka ONIIIIWAAA!
Yeah dude! I was stuck on it for days. I actually came closer to quitting the game from fighting Guardian Ape than Sword Saint. Funnily enough though, a bit later in the game when you have to take on another Guardian Ape PLUS a mini brown ape simultaneously, I was able to take them down first try. Who were your toughest bosses?
Which is your "second hardest boss?" Guardian Ape?