I havent gotten to fight Zeromus, Neo-Exdeath or Dark Cloud yet, but out of the ones I've fought, Necron was the hardest. Grand Cross made 3 party members Zombies and then he killed them with Neutron Ring leaving only Quina in critical. I couldnt resurrect them because they were zombies. Sephiroths Supernova was the only powerful move he had, but I got a Game Over after it because Cid was confused, and did a 4xCut on my party. Almost as soon as True Ultimecia appeared, she was talking (About to die). But Yu Yevon? that was too easy. He reduces his own HP to 1!!! and Zombie works on him as well!!! Bloody Hell!!!!