I just finished Persona 3 FES (I absolutely loved it, by the way), and I found Nyx to be a rather easy boss. I'd read so many posts on forums from people saying that the boss was "impossible", and that Moonless Shroud was the most unfair ability ever, but it didn't really prove to be a problem for me.
I was at level 75, and my party members were Mitsuru, Yukari, and Koromaru. The two Personas I actively used were Thor (with maxed strength) and Horus. I had my character using Mjolnir which, when Thor was equipped, dealt around 450 damage with each hit, until Nyx's final form when its defense was increased. When that form came around, I just switched to Horus, with Mediarahan (completely heals entire party) and Amrita (heals entire party's status ailments), and set my party to full assault. Yeah, Moonless Shroud was annoying, but I just set my party members to heal/support whenever Nyx put it up, and it was no problem keeping our health topped off. Granted, I did have eight Somas (item that heals entire party's HP and SP) and a bunch of resurrection items, but I didn't even have to use all of them.
I can see how the fight would be difficult for someone who was under-leveled, but you had a lot of time to level up and stock up on healing items before it was time for the fight, and you were given the exact date the fight would take place on. While I loved the game, and the ending, the final boss fight was a battle of attrition for me, and nothing more
I was at level 75, and my party members were Mitsuru, Yukari, and Koromaru. The two Personas I actively used were Thor (with maxed strength) and Horus. I had my character using Mjolnir which, when Thor was equipped, dealt around 450 damage with each hit, until Nyx's final form when its defense was increased. When that form came around, I just switched to Horus, with Mediarahan (completely heals entire party) and Amrita (heals entire party's status ailments), and set my party to full assault. Yeah, Moonless Shroud was annoying, but I just set my party members to heal/support whenever Nyx put it up, and it was no problem keeping our health topped off. Granted, I did have eight Somas (item that heals entire party's HP and SP) and a bunch of resurrection items, but I didn't even have to use all of them.
I can see how the fight would be difficult for someone who was under-leveled, but you had a lot of time to level up and stock up on healing items before it was time for the fight, and you were given the exact date the fight would take place on. While I loved the game, and the ending, the final boss fight was a battle of attrition for me, and nothing more