I can't answer for your FMV's all I can say it buy another game, your disc maybe too scratched.
As for the boss here.
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Name: Soulcage
HP: 9765
MP: 862
Level: 26
Weakness: Undead Killer, Fire, Holy
Items using Steal: Oak Staff, Magician's Cloak, Brigandine
Items dropped: Phoenix Pinion, Elixer
Exp: 0
AP: 9
Gil: 3800
Card: Antlion
Although this monster is vulnerable to Fire-related attacks, don't be tempted to have Vivi cast such spells: they turn the Soulcage's Leaf Swirl attacks into lethal Fire Blades. When in need, you can undo this by casting Ice-related magic or attack.
Actually, you'll find it very easy to defeat the Soulcage. Simply cast Life or use an Elixir on the monster to disable it instantly.
After the battle your party is automatically returned to the Outer Seal of the Iifa Tree. The Mist has dissipated, but just what does that mean? Now travel backt o Madain Sari.
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There so overall cast and use Healing related magic and items, try using a Phoenix Down aswell and get Garnet or Eiko to cast Life. And get someone to use Potions, Hi-potions, Elixirs etc..