Well, i watched on youtube some people fighting her but apparently the fight changed on the new version, she has 2 adds that keeps healing her with gravity 3. I tried "reflect" on her to prevent the heal from gravity but the adds gravity penetrates the reflect and just heal her. I dont die on this fight, but i cant kill her. I managed to deplete one of the adds MP, but the other seems to have so much more MP(infinite?). I just moved on and dont know how to kill her.
The two Flares are like a damage check. The best thing to do is wait until one is sent away for 'Take Over' (it'll remain on the screen, unlike the Nattak fight, but will become 'still' and inactive) and then try to burst down the remaining Flare with a round of strong attacks, maybe Summons or Limits. If it can't fully heal from Demi3 then you can keep pushing on it until it dies. When the other Flare comes back from Take Over, it'd be the same thing again; burst it down. If you've been able to get Quadra Magic from the Blue cave or W-Magic from Extra Battle then that can greatly boost your nuking potential. The key, though, is to make sure everyone acts as the same time; if a Demi3 goes off after the first hit then it will effectively cancel that attack out. If all three attacks land one after the other, though, then the Demi3 heal will be much less effective as it's based on the add's current HP.
This means you want to be stable against Mimic's attacks in the meantime so you can focus more on attacking. A White Cape, Hades + Added Effect, or Peace Ring can help defend against status ailments, while MBarrier will likely reduce down all but one of her magic-based attacks. When you've got the Flares taken care of, Mimic herself is weak to Holy damage so Pearl, Alpha, or Holy + Elemental in someone's weapon would be good choices. I can post a video taking care of the boss if you'd prefer a visual guide.
Kudos Chief on how pure evil you are regarding the level 4 limit bosses - I just can't seem to beat them, even at level 80. Any hints would be awesome.
Besides the Mimic notes above, I'd say Super Saver System is a good place to start. It's the weakest out of all the bosses, unless I've missed something about it. They've low defence/HP, weak to Bolt/Water, and only inflict a handful of statuses like Berserk and Death Sentence (though the Reflect might be a pain). And the Highwind Limit it drops is one of the strongest in the game.