Unknown / Unknown 2 / Unknown 3

Location: Sunken Shinra Plane (Genika)

Once your party has acquired the Submarine during the Huge Materia quests, pilot it near the shore of the Corel Desert.  The Gelnika is found on the bottom corner of the underwater cliff canyon.

Fighting Unknowns

You may need:
1x Ultima materia
1x Comet materia
1x Cure materia
1x Barrier materia
All materia linked with Cure or Barrier materia
Steal materia (Optional)
Morph materia (Optional)
Enemy Skill materia (Optional)
 

The Unknown likes to use physical attacks on your party, so cast Barrier early in the battle.  Begin damaging it consistantly by using high-power magic on it, such as Ultima and Comet.  Ultimate weapons for characters can be used also for a quick win.  When Unknown's HP is low it would use its Blaster attack, which damages around 4000 HP.  It would use this attack repeatedly until its MP runs out, but have Barrier will protect your members from all its attacks.  A Fire Armlet can be stolen, and Unknown morphes into a Power Source.

Unknown attacks
Bite
Tongue
Blaster

Location: Sunken Shinra Plane (Gelnika)

Once your party has acquired the Submarine during the Huge Materia quests, pilot it near the shore of the Corel Desert.  The Gelnika is found on the bottom corner of the underwater cliff canyon.

Fighting Unknown 2s

You may need:
1x Ultima materia
1x Comet materia
1x Cure materia
1x Barrier materia
All materia linked with Cure or Barrier materia
1x Heal materia
1-3x Peace Ring or 1-3x Ribbon
Steal materia (Optional)
Morph materia (Optional)
Enemy Skill materia (Optional)

Unknown 2's Abnormal Breath will confuse any one of your members, and may continue casting it until all your characters are confused.  Unknown 2 also has an attack called ? Needle which will paralyze party members.  Casting Resist or using a Vaccine will have your members immune to such attacks.  Cast Barrier on your characters and Regen, as Unknown's Tentacle attack can damage significantly, and Unknown 2 uses the attack repeatedly.  Make sure you cast Cure on party members when their HP is below 3000.  An Aurora Armlet can be stolen, and Unknown 2 morphes into a Guard Source.

Unknown 2 attacks
Tentacle
? Needle
Abnormal Breath

Location: Sunken Shinra Plane (Gelnika)

Once your party has acquired the Submarine during the Huge Materia quests, pilot it near the shore of the Corel Desert.  The Gelnika is found on the bottom corner of the underwater cliff canyon.

Fighting Unknown 3s

You may need:
1x Ultima materia
1x Comet materia
1x Cure materia
1x Barrier materia
All materia linked with Cure or Barrier materia
1-3x Peace Ring or 1-3x Ribbon
Steal materia (Optional)
Morph materia (Optional)
Enemy Skill materia (Optional)
1-3x Mystile (Optional)

Quickly cast Barrier and Regen on your party members.  Unknown 3's Creepy Touch move will inflict Sadness status on your party members.  Unknown 3 also use Poison Fang attack alot too, but equipping Mystile armor will certainly make that attack miss.  Unknown 3s Bolt2 and Slap attacks inflict heaps of damage if you're not careful.  Try to win the battle quickly by using Ultima, Comet2, Shadow Flare attacks repeatedly.  A Bolt Armlet can be stolen, and Unknown 3 morphes into a Magic Source.

Unknown 3 attacks
Poison Fang
Bolt2
Slap
Creepy Touch