The Ironclad is an enemy in Final Fantasy X, created in the Species Conquest at Monster Arena after ten Iron Giant and ten of each type of Gemini fiend have been captured. The prize for unlocking him is 60 Mana Tablets and the cost to fight him is 8,000 gil.
Ironclad's attacks are physical. His primary technique is "Reppageki" (剛剣法・烈破撃, Goukenpou: Reppageki?, lit. Unyielding Blade Technique: Buster Attack), a quick sword strike on one character that he uses as a counterattack in response to any damage. On his turn, he will use either "Bushinzan" (剛剣法・武神斬, Goukenpou: Bushinzan?, lit. Unyielding Blade Technique: Martial God Slash), which attacks all characters for both HP and MP damage, or his more powerful "Shinryuudan" (剛剣法・神龍断, Goukenpou: Shinryūdan?, lit. Unyielding Blade Technique: Divine Dragon Slice), a jump attack against the character with the highest current HP.
The best option is using the Celestial Weapons for defeating him.
Ironclad is not immune to Magic/Mental Break, however, it will only work 5% of the time, because of its Magic/Mental Break resistance.
While Ironclad is not immune to Armor Break, it will only work 5% of the time, so a Frag Grenade or Auron's Banishing Blade Overdrive (if successful) will be more effective against him with a 100% chance.
If the characters have Evasion of 200 or more, almost all of Ironclad's Reppageki attacks will miss.