People who didn't achieve to beat this mighty beast yet, here are some tips to use against Chaos:

1st Feral/Desperado Chaos:
The first Feral Chaos is tricky you don have much time. you have like 2 minutes before your Bravery attacks won't do anygood anymore. (It will multyply 90X) You have to deal with strong caracters to get his bravery down first and if he hit the max yust keep hiting him with Hp attacks.

Characters:
The caracter i only used to defeat this monster was the emperor. Use flare and trap cautioness and he won't have a chans to win.

2nd. Feral/Desperado Chaos:
This creature has over 100.000 live points, it's hard to get down with only Hp Attacks.
His Attacks are to been used to deplete all you ex and assist power when he attacks your Hp.

The Weakness:
His weakness point is his Bravery, when you launch a bravery attack it will do massive damage to his bravery. You can easy get 9999 HP Attacks. to deal him some damage.

The Caracters to use / Attack's to use:
The Easyest way to destroy this beast is to use alot of magic powers. So try to use Kefka or somebody else who knows alot of magic attacks to attack his bravery.
Or you need a real fast caracter with fast swordmanship like Sephiroth.