Like other winged Cie'th, they frequently evade physical attacks. They are usually encountered with other, low-ranking winged Cie'th and should be prioritized. Their powerful Lightning-based spell Levinbolt also deals heavy damage, and they are able to inflict Imperil to amplify the damage output.
Nelapsi and Krysta both have high Evasion, so it's hard to land physical attacks on them, kupo! Nelapsi uses the Wind Slash magic attack that deals wind damage to three random targets, and it has a moderate chance to Sap those hit, so don't forget to keep your heroes healed up with abilities like Regen. Both foes wield magic attacks, so although they resist break debuffs, keep the damage down using Heathen Frolic Sarabande and Shellga, kupo. Watch out when Krysta unleashes Miasma, as this deals magic non-elemental damage to two adjacent targets, temporarily lowering their Resistance. Krysta has a Slight Weakness to wind, so attack with abilities that deal that damage type, kupo! Neither foe is resistant to Slow, so Slowga is a good debuff to bring to the battle! Just bear in mind that Krysta is Immune to lightning, kupo. Defeat all enemies to win the battle!
Cocytus, along with Nelapsi, appears as a boss in the "Academia 400 AF, Part 2 (Elite) New Town, Part 1" Final Fantasy XIII-2 realm dungeon. However instead of Cocytus, the boss is named Krysta. This change is most likely being due to the localization team for the game reusing the same English name for the Krysta boss from Final Fantasy VIII, which are both named Cocytus in Japanese.
- Lightning: Deal three moderate magic lightning attacks to random targets.
- Lightning: Deal five moderate magic lightning attacks to random targets.
- Miasma: Deal magic non-elemental damage to two adjacent targets, and temporarily lower their Resistance.
Cocytus, meaning "the river of wailing," is a river in the underworld in Greek mythology. In Dante's Inferno, Cocytus is the ninth and lowest circle of Hell where traitors are frozen in a lake of ice, Satan is imprisoned waist deep in ice at the very center of Hell. There are several other new Cie'th in Final Fantasy XIII-2 named after elements from Inferno, which lends weight to it being the intended reference.
- The Cocytus is the only winged Cie'th with a signature spell in Final Fantasy XIII-2.