The Elite Four in Pokémon (they'd count as a boss, right? )
I almost always have trouble with them. I'm not sure what X and Y is like, but the Elite Four is always a challenge for me. Cuz I always spend hours buying revives and medicine while also figuring out what lineup of pokémon I'll use and training them for days just so they are all at an equal level and are on the sane ball park as the Four's pokémon. I try using a system, but it's no good. I always end up losing constantly cuz of something I forgot, like paralysis heals. Plus, I get stressed thinking that I gotta beat them all in one go and if I fail, it's back to the start
I know others have no bother, but I'm not very good at the game, so I just can never seem to master this part. I always win by sheer trial and error. And by the time I am able to beat them, I don't even know what I did different XD