On disc 3, right after you get the Ragnarok go to the Centra Ruins and put on Diablos' Enc-None, unless you want to fight Tornberry (that's a different story...). Go up the stairs and you will see a statue. Select the option [Take out the eye] and write down the code that comes up on the screen. Then keep on going up and you will see a statue with one eye. Put in the eye you have and then take both eyes out and write down the code that appears on the screen. Proceed up and then you will see a statue with no eyes so put both of the eyes you have in. Type in the code and Odin shall appear. Fighting Odin is easy because he doesn't attack but you'll get the Odin Card if you beat the time limit. After you defeat Odin he'll appear at the beginning of a randomly chosen battle except boss fights. In the last fight with Seifer, on the Lunatic Pandora, Odin will fight him but Seifer will see him coming and kills him. But Odin's sword is taken by a Legendary sword collector, Giglamesh. From now on Giglamesh is yor Odin except his attacks can vary, he can come into boss fights, and he appears any time in battle.