'Bah!', you say. 'Non-bonus RPG bosses are easy because you can always just level grind until you're powerful enough to beat them!'. No. No you cannot. Because going into Zophar's castle is a one-way ticket. No shops to resupply, and nothing that restores MP and the item cap for everything is 15 if you try to max out beforehand. There are a lot of regular and mini-boss battles on the way to the top floor which will most likely deplete your stock somewhat. Finally, like all other bosses in this series he gets increases in attack power and HP the higher your own levels are.
Furthermore, no amount of grinding will ever give you enough HP to survive his single-target 'laughing' attack (4-digit damage in a game with a 3-digit HP limit; at least his animations telegraph it). He is the only boss in the game to consist of five separately-acting portions (even the five-headed dragon boss from earlier only got one action per round), and each portion has more HP than any other boss up to that point. On average two of them use powerful all-hitting spells while the other parts will either hit you for medium damage, heal the head or DRAIN YOUR MP TO ZERO. And only one of your party members is a dedicated healer! If he is drained or killed by the 'laughing' attack, at least one of your other four party members will probably die before you can use an item to revive/restore his MP and get back to healing. If you're out of them... you dead.
Need more proof? There's exactly one video on Youtube of someone beating him. It's split up into 5 parts (fitting) and around part 3, three out of five of the guy's party members are dead and he's spamming the rarest revival items in the game just to be able to keep up with all the damage. Finally, he's completely invincible for the first six rounds or so for plot reasons. But he still attacks you, albeit only with two of the limbs and not as strongly as when the real fight starts. GREAT uplifting battle theme, but the hardest battle I've seen in an RPG. I've managed to kill one or two of the limbs occasionally, but always run out of steam before being able to deliver the coup de grace to the head and the remaining pieces.