Part 16

From the Passage, turn left and open the chest for a Mythril Shard (2/20).

Continue down to another chest containing an Ether (4/20).

Defeat the Heartless and proceed down the steps to a chest with an AP Boost (5/20).

At the end of the path, turn around and go back up the neglected path.

Open the chest for a Hi-Potion (6/20).

Head to the end of the Passage to find another chest with a Mythril Stone (3/20).

In the Inner Chamber, find the book labeled "Absent Silhouette" and two chests containing the Underworld Map (7/20) and a Mythril Shard (8/20). You can fight Zexion's Absent Silhouette later.

Head into the Valley of the Dead.

Fight your way up the three platforms, encountering Creeper Plants.

In Hades' Chamber, join forces with Auron. Attack Hades to start a scene.

Fight your way back across the Valley of the Dead. Use Auron's Limit against the Large Body on the third platform.

Fight back up to the entrance; the way back is locked, and Cerberus appears.

Defeat Cerberus. Target one of its heads. Use the "Evade" Reaction Command when Cerberus smashes its heads together, leading to "Jump" and "Dog Paddle" for damage and stun.

After defeating Cerberus, head to the Coliseum to meet Hercules.

Receive the Coliseum Map after the scene.

Speak with Phil in the arena to begin training.

Phil's Training - Round 1: Get 20 orbs from pots in 90 seconds.

Phil's Training - Round 2: Focus on large pots for 30 orbs each.

Upon completing all training, you will learn Aerial Dive.

Approach Hercules after training is complete.

Head back to the Underworld Entrance; the flames have dissipated.

Open the chest for a Power Boost (1/20).

Head to the Underworld Caverns.

Jump off the cliff through the smoke and collect Heart #9.

Defeat the Trick Ghosts that appear.