Ice Titan

Ice Titan
Location: Olympus Coliseum
How to find him: After beating Hollow Bastion the first time, go back to the Coliseum. Beat the Hades Cup (if you haven't already) then, talk to Phil, and when asked what Cup you want to compete in, choose the top ????? option. This is actually the Gold Match against the Ice Titan. Be sure you have half Ethers, half Potions equipped. Also, you MUST have the ability Guard equipped

The Ice Titan is the easiest optional boss.