Reviving General Leo, not a problem! Apparently there are a number
of ways to do this. Keep in mind that these are purely speculation of many players.
Fight 4000 battles in the dino forest after killing
the Gold Dragon. Don't get Gogo or Umaro. Get level 99 on all characters.
Fight 255 Brachosaurs in the dino forest after killing the Gold Dragon. Don't get Gogo or Umaro. Get level 99 on all characters.
Fight in the dino forest after killing the Gold Dragon. Don't get Gogo or Umaro. Get level 99 on all characters. There is a 1/1400 chance you will fight a Gold Dragon.
Fight 255 battles with Atma Weapon equipped. Have the Ragnarok Sword in the items list the whole time. Don't unequip the Atma Weapon.
Want some proof that you can do this? Then keep reading!
Try glitching the game with Relm's Sketch ability, and Leo may appear as one of the characters. Use any magic spell, and Leo has his own casting stance. Try it out!
Mail me if you wish on this.