In the sky castle, there is a long bridge just before fighting Tiamat. On this bridge it is possible to fight an enemy even more powerful than Tiamat herself, called Warmech. Warmech has 1200 HP and can cast some mean spells. If you encounter it, just use Nuke and fight with your Master Knight or Ninja. Heal with the white mage. The warmech is a powerful foe and fighting him is optional. If you can kill him than you truly are a Final Fantasy Master.