This esper you will find in Necrohol of Nabudis behind the Door of Despair, but to have it opened you need to collect three Medallions (Medallions of Power/Might, actually) (look in "Nabreus Deadlands" part) and defeat Fury and Humbaba Mistant in Necrohol of Nabudis (look in "Bosses not connected with the Plot" part).
About 195 000 HP,
Chaosjets have 4079 HP
Resistant to Libra,
Vulnerable to Earth,
Vulnerable to Sap,
This is a very tough opponent, because you are not allowed to use normal attacks in this battle. Chaos starts the battle with four helpers called chaosjets. Each of them have an elementary weak point, but it is not worth to attack them with elementary spells. The best way is to attack them at one time with Scathe (if you have it already) or different (but not elementary) spell.
Do not forget to set all gambits connected with mana to: "Self: MP<10% ---> Charge" before the fight. The wizard that has the biggest magick rate, should have Rose Corsage, to keep his spells unstopped by Chaos's silence spell. Others can also use magick if they are able to, but they should keep the main wizard in a good health condition.
After killing all Chaosjets, take care of main dish, Chaos I mean. His attacks are:
- Whirlwind - wounds everyone in its range with the power of wind,
- Aeroja - when normal Aeroga wounds everyone in its range, Aeroja wounds everyone without exception, plus it also can cause Confuse,
- Fearga - decreases MP, at everyone in its range. Luckily Chaos uses it at the end of the battle.
- Enrage - increases swiftness of attack and amount of normal attacks that opponent can mix in one combination.
What's more, he helps you when uses his normal attack, because it also has an influence on him.
At the beginning cast Bleed or Scourge spell on Chaos. That causes Sap. The good idea is to use Shear too, which decreases his magic defense. The only one thing left is to attack him continuously.