To be honest I found Neo-X-death easy. I beat him on my second try. I suggest you get ribbons to avoid his Grand croos attack. I found 2. One fron a girl in the armour shop of Mule and the other I think was somewhere in the Celft of dimension.

Here is what I had.

Bartz
Bare
Masterd Time Mage
Masterd Knight
Abliltys:
Time
Store (But this one doesn't matter)

Reina
Bare
Masterd White mage
Masterd Knight
level 2 Samurai
Abliltys:
White
GP toss

Faris
Mime
Masterd Summoner
Masterd Monk
Abliltys:
Summon
HP+30%
HP+30%

Krille
Bare
Materd Black Mage
Masterd Geomancer
Masterd Knight
Abliltys:
Black
Earth

Have Bartz use Meteo. Reina do GP toss or heal if soneone is low. Faris summon Bahumat or if his turn is after Reina Mime. Krille use either Ice3, Fire3 or Bolt3 or use Earth. Give Reina and Faris a Ribbon and have these waepons euiped. Masume, Exlibur, Chicken Knife, Assain.