Well all my character are at lv59+ and i am still not able to defeat him. He can use Big Bang twice even before i can revive and heal the fallen character. Definitely the cheapest of all Final Fantasy boss. At first i thought FF5 Exdeath is strong but Zeromus is even more hard to defeat. Any good advice?
If you don't feel like using a thought out strategy, you could just take both Porom and Rosa with you. With them spamming Curaja while the front row people attack/throw, you should win without too much trouble. If you need more tips, this topic should help:
Have you beaten all the rest of the bosses in the Lunar Subterrane and gotten the Crystal and Dragon armors?If so, you'll be fine.
For the most part, I would leave Rydia dead. She's practically dead weight in this battle since Zermous counters Black magic and Summons with Flare or Bio. Not to mention that she can't even withstand a single Big Bang with that 900~1200 HP she has.
Edge should throw crap like the Excalibur, Spoon/Knife, Fuma Shurikens,and old weapons. Edge is mostly here for extra muscle.
Cecil,Kain, and Rosa are the main 3 you should focus on keeping alive. You can keep Edge if he doesn't slow Rosa down, but the less people you have, the more Curaja will heal.
*Bad guy picks up phone*Phone: You are receiving a collect call from:CAPTAAINN CAAAAAVEEEMAAAAAAAAANNN!!!~Robot Chicken