Hmm, possibly a stupid question. *Spoilers possible I guess*

[ValiantKnight]

/nod
Tried again at 62/62/64/62/60

He still beat me up pretty good.
Rosa has to Cure4 or Cure3 every turn.. period.. no matter what.. end of sentence... Rosa doesnt get the luxury of casting life2 or any other spell than group cure3/4.

Double big bang kills everyone but cecil and kain.. and then they die trying to revive others.

Zeromus even at a 5 speed rating(6 is slowest) still gets about 3 turns to Rosa's 1. This almost ensures at some point that he will get a double big bang inbetween Rosa's Cure4s. A double big bang at this HP level = death.

Edge threw excalibur and Knife, then died. Rydia summoned bahamut once, then died... 2800 hp vs 1700-2600 big bang = nope...
Kain lived for a while but died cause he cant be healed while jumping.
At one point it was just Cecil and Rosa, and rosa could keep up with the damage with just Cure3, but Cecil would need to kill ugly in 25~ attacks or less and im not sure his 4000 per round is enough.

When I get bored, I'm going to try it once more with just Cecil and Rosa, and no one else.... not sure how im going to work that to make sure the rest die and they dont. perhaps then I will have the speed and mana efficiency to last long enough to kill him.....
Speedy pain in the.. he is.

It's got nothing to do with his damage.. it's just my parties inability to take 2 big bangs and rosa's inability to fully heal 5 characters for a full big bang.. and Zeromus's insane speed to give him the ability to at some point get 2 big bangs in there.

*edit*
Lvled to 66/66/68/66/64
Rydia now with 3300hp, Edge/Rosa at 3800, Cecil at 5000, Kain at 4700

Set it to slowest batspeed and msg speed.

And for some reason he didnt big bang this often this time.... He never killed more than 2 characters. Rydia summoned everyone back with a life1 asura late in the going.. and Rosa's cure4 augmented by Cecil's Cure2 with an elixir from edge or kain now and then to keep rosa alive. 5 bahamuts, 4-6 cecil attacks, throwing excalibur, fumas, and knife, and a few jumps from kain later...

Nice ending
He's still rather hard compared to any other FF end boss i've played besides possibly FF9.
FF1, 6-8, 10. Tactics had some really tough ones too though.

Now.... To try for the pink tail..... lvl to 99.... or .... switch to another game:

FFX(beaten... need to complete more of the sphere grid and beat Ultima Buster and the final monster arena fight)
FF6(I had gotten all the way to the final tower and had a save point just before... lvling up to get a little stronger as I was low 40s and getting my rear kicked a little.... then lost the save to corruption... so starting from scratch)
DQ8(finish getting my 99/99/93/99 party to 99 and maxing skills from stealing seeds or restarting a new game)
FF5 or FF2(havent started either)
or something else