Pteryx has Auto Regen. It will evade most normal attacks, unless the character has a high Accuracy stat. Its normal Beak attack inflicts Delay (strong), and the special Beak of Woe ignores the Protect status while inflicting Curse. Pteryx will open the battle using Beak of Woe on all party members in one turn, then afterwards target a party member without Curse or use Beak if all party members have Curse.
Pteryx can be easily defeated using Wakka's Attack Reels. Celestial Weapons are not necessary, although they make defeating the Pteryx much easier, as the damage limit is broken and so Pteryx can be defeated in a small number of normal attacks.
While Pteryx is not immune to Armor Break, it will only work 10% of the time. A Frag Grenade or Auron's Banishing Blade Overdrive work 100% of the time, and so are more effective to break its Full Break resistance.
Pteryx is Greek for "wing". Pteryx is also a genus of beetles in the family Ptiliidae.