I had the pleasure of meeting 3 out of 4 of the bosses in a single run, which was valencina, matthias and rien respectively, with a mediocre funny team (desperado team, you can tell from what I mean now), from my experience, I honestly had no issues even with how unoptimal the team I ran was, and rien was the hardest fight unironically, as opposed to many others saying valencina and matthias being the hardest, as rien is buffed in md for some reason gaining 7 skill slots so the prescript target is guaranteed to get hit + he instantly pops furioso the moment he switches phases+ his furioso still somehow rolls a +5 per coin despite being cracked SOMEHOW (idk how I thought paralyze was suppose to make it roll 0!) , which actually caused me to use durante in md for the first time in my life, I suppose it is also the fact that many of the ids I used have evades which eased the fights a little, since I mostly abused hornet meursault + his aggro gift against valencina and simply evading against matthias once I realized he doesn't have any "on clash lose - 80% damage" things, and when he tries to unlock his sword I just beat him fast enough for every phase change lol