Kingdom Hearts 2.5 Walkthrough Part 1 - Olympus Coliseum

#	Treasure	Location
01	Power Boost	Underworld Entrance. After the training session with Phil.
02	Mythril Shard	Cave of the Dead Passage. Go west at first fork and look east.
03	Mythril Stone	Cave of the Dead Passage. Near Inner Chamber exit.
04	Ether	Cave of the Dead Passage. Push west past Treasure 02.
05	AP Boost	Cave of the Dead Passage. Further on path past Treasure 04.
06	Hi-Potion	Cave of the Dead Passage. Head east at first fork.
07	Map	Cave of the Dead Inner Chamber. Next to save point.
08	Mythril Shard	Cave of the Dead Inner Chamber. Near the Passage exit.
09	Hi-Potion	Underworld Cavern Entrance. Return here from Lost Road.
10	AP Boost	Underworld Cavern Entrance. Return here from Lost Road.
11	Mythril Shard	Underworld Cavern Entrance. Drop into fog to a ledge.
12	Hi-Potion	Lost Road. Push west from starting point.
13	Ether	Lost Road. Seen near a wall to east from starting point.
14	Mythril Shard	Lost Road. Go right near Atrium exit.
15	Mythril Stone	Lost Road. From start go around left then right.
16	Tent	Underworld Cavern Atrium. Go right from starting point.
17	AP Boost	Underworld Cavern Atrium. Climb stairs beyond the fog.
18	Caverns Map	The Lock. Seen next to wall on the right side.
19	Mythril Shard	The Lock. Seen next to wall on the right side.
20	AP Boost	The Lock. Seen next to wall on the left side.

It's been a while since Sora has paid a visit to this world, but instead of starting off at the Coliseum, he touches down in the Underworld—the home of Hades instead. The first person you will meet is Megara, Hercules' unofficial girlfriend. You'll find her on her way to speak with Hades about easing up on the trouble he's causing because Hercules is having a tough time beating down the monsters being thrown at him.
Sora offers to go talk to him instead, and the crew enters the Cave of the Dead. Fight through more baddies, all the way to the Valley of the Dead. Hades mean while summons Auron from the dead, and tries to force him to join his cause. Auron rejects him and escapes. Sora soon meets up with Auron, and every takes-off back toward the entrance of the Underworld.

 

Waiting on the crew is an old and nasty foe from the past - Cerberus. You cannot use your Valor drive form in the Underworld but you can use your limit attacks Take advantage of Sora and Auron's combo limit ability as much as possible, and Cerberus should be taken down in no time at all.

 

Go to the Coliseum and meet up with Hercules. Also, go chat with Phil to get some hero training under your belt. It isn't long before Hades stirs up some more mess, and both the Olympus stone and Megara go missing. Sora and the team heads back to the Underworld to take on Hades.

 

On your way back on along the path you previously walked along, you will run into someone from the Organization XIII. Don't sweat just yet. This guy, for the most part, is a pushover. He will send 100 water clones of himself at you that you must dispatch in 80 seconds. This is a simple task if you make use of that Triangle button as much as possible. Take all these guys out will result in Demyx's defeat. He gives up the Olympus Stone and you can go free Megara now, who happens to be sealed inside a giant stone. At this point you have to step in a green light, and enter a fight with Pete!

 

There are two phases to this battle. During the first, just worry mostly about the flying Heartless that are causing trouble. But keep Pete away from Megara, who will be running around the battle area helplessly. When he is close to her, go upside his head with the Keyblade to distract him and remember to move when he gets all enraged. Eventually Pete decides to hang back for a second, and Hercules shows up to lend some help.

 

You only got 2 minutes to win so remember to ignore the heartless this time around and focus on Pete. Repeatedly use that Triangle button to counter Pete's attack. When you know him off balance, pop him in the head with a couple of thrashes from your Keyblade. If he tries to drop a rock on your head, run to Hercules and activate the shield. But in the end, this altercation shouldn't be so tough. Remember to stay aggressive.

 

Soon you'll face the Hydra. This fight isn't nearly as bad as it looks. You just have to wait for the beast to drop his head so you can pop him. When he's dazed, run up and hit that Triangle button to finish him. After that, you'll see 3 other heads pop-up. At this point you can run up on the Hydra's back and use an attack with the Triangle button. Once you take out these three heads, you'll deal with seven. Don't fret because Pegasus is willing to come through and help out with an attack activated by the triangle button. You can also hit his head when he drops it low enough.