Baron doesn't really count since I killed him on first try I think, hydra was easy because I was a hydro, mayor was easy, 2 blood hounds + specialist/caretaker (forgot) was probably hardest.
At level 30 my hydro can solo EVERYTHING except for them with ease, I almost die trying to solo them...
Oh and 2 armored hounds + ZPCI elite on my hydro's legend run, and the warden was annoying...1.4k hp and taking out half your hp with the speed reducing + double turn...
twisted experiment? hes easy: ive tryed to beat this guy took me 100 training fights(oh yeah i did count) when a guy that came to my house played he gave me his legend game, got it up to boss of z7: the corrupter.
he hits 5000s, and he has these orbs that heal 8000, and if u kill one of the orbs, the corrutper turns into his true form, all attacks to him deal 10000 less (so if u hit a 10002 normally), it would hit a 2.
hes impossoble (even with 100 training fights i just used a heal and fight tactic, only 1 health left, i kept silenceing the orbs (well i was hydro so i was mind freezing or stunning em.)
My hardest Enemy? Well i can't really say.But because i want to tell something, I'll say that it is all those who post Cheating pvp codes and tell us to beat'em...What? You said in sonny 2 not in the single player of sonny 2!
I never found the Baron or the Twisted Experiment to be that hard as long as you train beforehand 10-15 fights. The most challenging fight by FAR is Gregor. Not high HP but insane healing buffs. Had to start from the beginning of the train in order to get back to it.
Hardest is the warden at heroic difficulty. Baron is not even hard if you just drain his focus and every time he does tick-tock just put ice wall and you lose only about 40% of your life and it's not very much to heal (works only as hydra).