You can unlock Vidatu by capturing four of each Imp-type fiend, which includes each of the following:
HP: 95,000
Vidatu is heavily magic resistant, and very few magic spells will work against it. That said, you can still use 
Holy, 
Flare, Drain, or Ultima. Even with magic resistance, though, Vidatu is relatively easy to take down. Use 
Mental Break if you’re having trouble.
You should consider power leveling your characters and obtaining the Celestial Weapons, in this case, for Yuna specifically. Check out the Advanced section of the Tips and Tricks for more information. With properly leveled characters, this fight is pretty straightforward.
| Ability | Description |
|---|---|
 Sensor |
“Immune to sensors.” |
 Scan |
“Immune to scans.” |
Steal:
Lightning Gem (x4) (common)
Mana Tonic (rare)
Drops:
MP Sphere (common)
Dark Matter (rare)