HELLLP MEEEEEE on Zanarkand Trials!!!!!!!!!

I have gotten to the Zanarkand Trials and I have Followed Braska, Jecht, and Auron's Ghost Selves, I have beaten the Trials, have not beaten the monster that you mut fight right AFTER that. I do not have any Mega Potions or Mega Phoenix Downs, though I do have about 200,000 Gil, but I am saving for when I go back and get the Summon in the Cave right between The Calm Lands and Mt. Gagazet in the little Valley below the Bridge. Is it possible to beat him without any Mega Phoenix or Mega Pots? My Auron is Maxed out, my Tidus is almost Maxed, Kimhari is Close to maxing out, Rikku is way beyond Maxed, and I have her in Aurons Sphere Grid to get her str up, Yuna doesnt even have Cura, making me kinda feel like a noob :/. Wakka is about 2 Grids away from his max stats, Lulu, I havent worked on since I got her Daga Spells. Anyway I can defeat him without going back to get anything or Train? if there is, please post. I will go back for items and training, might even get Auron's Ultimate Weapon if I can't do anything.