richboywonder, just keep in mind that the additions to the GBA version aren't in the other versions of the game.
dappa, Zeromus EG is the final boss at the bottom of the bonus dungeon in the GBA version.
I found Zeromus EG somewhat of a disappointment, since he has an attack pattern. Once you know his pattern, it's easy to preempt his attacks, and plan accordingly. Healing after Tornado, Big Bang isn't a threat anymore except for the HP drain, and his scary triple-spell combos aren't very damaging at all. The only tough part was his big physical attack combo, which can really hurt your lower defense characters. I beat him with party in the 60 or 70s, if I remember.
He'll also only use Absorb when he gets weak...so just keep pounding on him when that happens, as he's almost done.
Also, there exists a bug when you use the Grimoires you get from the Lunar Trials on Zeromus EG. They'll use seemingly random spell animations and even turn ZEG into a toad. So if you want to make him easier, there's always that.
