Oceanus is the second layer of the Underworld route — a vast subterranean waterway flowing beneath the earth. The area is dominated by rushing water, cliffs, and bioluminescent underwater caverns. Chronos has twisted the sea creatures of this realm into hostile forces.

Water-type enemies here can attack from unusual angles, making positioning more important than in earlier layers.

Scylla and the Sirens fight as a coordinated trio, combining ranged musical attacks with close-range melee from Scylla herself. Managing which Siren is active while avoiding Scylla's charge attacks requires careful prioritization.

• Driftwood (tool upgrade material for Rod of Fishing)
• Pearl (mid-tier crafting material)
• Cattail seeds (for Crossroads garden)
• Feathers (Gale familiar upgrade material)

Area-of-effect boons help deal with the Sirens' spread-out positioning. The Sirens must be neutralized before focusing on Scylla to reduce incoming damage.