How do I beat Zeromus?

When fighting Zeromus, your characters should be level 58 or above. That is when I beat him. Have Rosa, Cecil, Edge, Kain, and Rydia in your party. Equip them with their ultimate weapons. Have Rosa casting curaja on your whole party after Zeromus uses one of his attacks, like Big Bang or Malestrom. Have Edge throw shruiken and all of your old swords, (dont worry, you will get them back because the game doesn't save after the battle, it just gives you a star and unlocks the lunar ruins). Have Kain jump, have Cecil attack, and have Rydia summon Bahamut. Also, bring elixrs and megalixers. This should garuntee easy victory.

I tried.that and lost I lvd up to lvs 71-77 and I can't survive big bang

Yeah. I used cheats. On my 2nd try Edward died (he was lvl 54) ugh. BTW my rydia and Edward cheats for lvling up fast don't work...

I did it with Cecil at level 50 and Rosa at 49. Both of them have the best equipment. Kill off all party members besides Cecil and Rosa before using the Crystal. Cast Cure 3 or Cure 4 after every attach by zeromus (wait until he attacks). Attack with Cecil every time and have him use an elixer or ether on Rosa as her magic goes down. All the other characters just spread her magic too quick and you can't recover them quick enough. This is for SNES, but probs works for other games too.