"Its shell deflects physical attacks well. Tentacles absorb magic attacks. Defeat tentacles first, then force it from its shell with fire magic. Absorbs water-based attacks."
Sinspawn Geneaux is the third Sinspawn encountered in Final Fantasy X, left behind after Sin attacks Kilika. It is assisted by two Tentacles which sprout from the ground on either side of the player party.
The tentacles will intercept any spells directed at Geneaux and their attacks will inflict Poison. Geneaux will initially stay inside his shell and is protected against physical attacks. Once the tentacles are defeated it is quite vulnerable to magic, particularly Fire. When its HP drops past 2,400, the shell will open and Geneaux will begin attacking by using Poison and Water-based spells, which can be countered by using Wakka's Silence Attack or Yuna's NulTide spell.
Now that it can be hit physically, Tidus and Wakka should be able to finish the battle easily. Before leaving Besaid, head to the beach then return to the village shop. The clerk should mention that her dog " found something strange", find and examine the dog to have Valefor learn a new overdrive called "energy blast". This will easily overkill both tentacles and Geneaux in one hit as soon as the fight start.
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Concept art from Final Fantasy X Ultimania Omega.
Sigh.
Staccato.
Venom.
