The Centra Ruins are a big weird structure in the northeastern part of the Centra Continent. PUT ON ENC-NONE and go inside after you get all of your characters’ HP to critical status (yellow letters). When the stairs split, go right. Examine the stone block in the center of the room to ascend. Take the ladder on the left, examine the orb. Climb down the ladder, examine the second orb and this will reveal a staircase. Go up the stairs. Once up the stairs, take the first ladder on the left and take the LEFT EYE from the statue. Climb down the ladder and go up the stairs on the right. Put the eye in the statue top get a password. Take both eyes and return to the first statue. Put both eyes in the first statue and enter the password, top to bottom.
Go through the open door and fight Odin. He won’t attack you so don’t worry about strategy. He will just sit there, so draw Triple if needed, and unleash the limit breaks (since you kept your HP in critical status). Beat him before the timer runs out. He isn’t like a normal GF, he will, rather, appear randomly in battle with frequency depending on your character’s luck stats. Once you get him, fighting Seifer at the end of Disc Three will obtain you Gilgamesh, who will replace Odin as a more powerful deus ex machina type of GF.