|Final Fantasy X Boss|
|Sensor||Covered by hard thick shells. Vulnerable to magic.|
|Location||Submerged Ruins - Underwater Hall|
|Common Steal||Water Gem|
|Rare Steal||Water Gem|
|Common Drop||Power Sphere|
|Rare Drop||Power Sphere|
|Weapon Drop||No Encounters|
|Abilities||1st Encounter: Physical attack only|
2nd Encounter: Stone Punch, KO Punch, Swallow
|Resistant to||Poison (95), Zanmato (Lv. 4)|
|Immune to||Silence, Sleep, Darkness, Petrification, Slow, Zombie, Power Break, Magic Break, Armor Break, Mental Break, Threaten, Death, Provoke, Doom, Scan, Gravity, Delay, Eject|
|Other Information||Fought underwater.|
The party cannot escape.
- "I'd made it out of the frying pan, and into the freezer."
- —Tidus escaping Geosgaeno the first time
Geosgaeno is a geo-type fiend in Final Fantasy X, which appears on the Baaj ruins to threaten Tidus when he tries to find shelter in the ruins of a temple near the beginning of the game. After three turns, Tidus wisely decides to flee. Later on, once the party has gained control of the Fahrenheit, the ruins can be revisited, and Tidus, now accompanied by Wakka and Rikku, can attempt to defeat the boss and enter the Chamber of the Fayth which houses the fayth of the hidden aeon, Anima.
Geosgaeno can drop weapons with No Encounters, and armor with Auto-Reflect. Since No Encounters cannot be customized to a weapon, only an armor, defeating Geosgaeno is the only way to obtain a weapon with the Auto Ability in the game with a 50% possibility of dropping it.
When encountered in the beginning of the game, Geosgaeno's every attack simply halves Tidus's HP. After three turns, a cutscene will play and the battle will end. If the monster is killed (which is only possible through use of a cheating device such as GameShark to alter Tidus's stats), the cutscene will play as if the battle had ended normally.
In the later battle, Geosgaeno attacks with Stone Punch, causing Petrify. Because the fight takes place underwater, the characters will instantly shatter, making them inoperable. In addition, Geosgaeno uses the ability KO Punch, instantly killing a character. It is advised to have armor with Stone Ward or Stoneproof, as well as Death Ward or Deathproof. Geosgaeno also inhales one character occasionally. When this happens, all positive Statuss, such as Protect or Haste, will be applied to Geosgaeno so long as the character is still contained within it.
The inhaled character may Struggle or Defend. If the one inhaled does not Struggle, the next turn Geosgaeno gets, it will exhale, bringing them to 1 HP and knocking out the other two characters. If they do Struggle, Geosgaeno will exhale and only KO the one who was swallowed. If a character is swallowed and Geosgaeno is defeated, it will cause 9,999 points of damage on all characters. This means one should never defeat Geosgaeno if a character is swallowed.
When encountered in the beginning of the game, one should not waste turns and Potions healing, as every attack simply halves Tidus' HP. After three turns, a cutscene will play and the battle will end.
For the later battle, a simple strategy for the later boss battle is equipping a weapon with any elemental affinity (e.g. Firestrike) onto Tidus and use Quick Hit. Hastega is also a good option. Rikku can Use Elemental Crystals and Wakka can use his Overdrive Element Reels. Geosgaeno has relatively low HP.