Everyone was around LVL 40, Aeris a bit lower, even though all were on backrow, the Red Dragon would still deal around 3200 HP DMG when he did the physical biting attack. Everyone has the HP Plus materia but far from leveling up so most of the characters HP were around 2800. What I always aimed to do was trying to get everyone of the Big Guard Enemy Skill but most of the time he would kill one of the characters and I had to go back to rezzing and healing.
The main problem that I had with this boss is that he was invulnerable to the Added Effect + Choco/Mog materia combination, to be honest I never really use summons and magic to beat bosses, all I do is put Big Guard on the character that has that combination on his weapon and wait for the boss to be stopped, once that happens I start hitting with deathblow and everyone else hit with their physical attacks while all are on haste.
The materia I needed was Barrier, I would equip Aeris with Barrier + All and do it asap when the battle started, after that was done the battle was mine.
I avoided using Big Guard because it makes the barriers go out too quickly, it only works for one character and whenever I did Cure2, it was halved due to the magic barrier.
Also equipped one character with with Fire ring, the other 2 with Elemental + Fire to be immune to his breath attack.
Set Cloud with his LVL 1 Limit so I could use Crossslash to paralyze him even if it was for a few seconds.
What did you guys do for the Red Dragon?
Been working a lot lately which is why I still haven't gamed yet, if I get some time tonight, I'll take on the wall monster again, I died the first time and haven't gamed yet