Though the Dark Pit issue is left unresolved, Palutena needs Pit to focus on the Underworld Army once more. Today’s target is Tanatos, the God of Death himself. He leads Medusa’s invasion of the sea, and so Pit must cross the desert, enter the sea, and take from Tanatos the Underworld Key. Right away, you encounter fierce resistance. Expect pretty much everything you’ve seen of the Underworld Army thus far.
When you arrive at the sea, Palutena parts it using her Mystical Powers of Sea-Parting ... which really just involved a call to Poseidon, the god of the sea. This also marks the beginning of one of the hardest sections of the Air Battle. Zurrets, Toxiecaps, Octos, Brawny Claws, and Gyrazers fill the tight passages of the parted seas, and just trying to dodge everything they throw at you can be very difficult. Use your Special Attacks if you’re feeling too much pressure. Consider it a reprieve when Palutena says it’s time to go deeper, as the enemy numbers thin out considerably.
You eventually pass through a cave network that leads to a city that was sunk by Poseidon. If you’re low on health here, Recovery Orbs will arrive as you pass through the ruins.
Watch for a Snong shortly after Palutena announces you’ve arrived at the ocean floor and prioritize destroying it as quickly as you can. The Seafloor Palace is not very far from where you encounter this monster, so just hold on for as long as you can.