Mission 90: Place the device

Mission 90 in Kingdom Hearts 358/2 Days sends Roxas to Agrabah to plant a mysterious device for Organization XIII.

Summary
Install the device we provide you with in the Lamp Chamber of the Cave of Wonders.

Objectives

 * Place the device!
 * Defeat all the Heartless!

Story summary
Still worried about Xion, Roxas is deeply troubled and begins questioning himself about who he really is. Nevertheless, he is sent on another mission, this time to Agrabah to plant a device. After the mission, Roxas wonders why he’s working so hard for an Organization that won’t answer his questions. He asks himself if he has anyone left to trust and sheds a tear before leaving.

Meanwhile, Mickey wanders through the woods, when he encounters a hooded man. The man removes his hood, revealing himself to be Ansem, Seeker of Darkness. Mickey prepares his Keyblade for battle, but the man puts on a blindfold and transforms into Riku.

Mission walkthrough
Defeat Heartless in every room while traveling to the Lamp Chamber. Once at the Lamp Chamber, Roxas sets up a device in the chamber on behalf of the Organization. However, Heartless appear in an attempt to destroy the device. To move on, Roxas must defeat them. The Heartless battle shouldn't be that hard, but watch out with the Land Armor. The Land Armor is highly susceptible to Aero magic. Limit Recharges, Potions and Cure magic are a good idea. Whittle away at his HP until you are victorious. After the battle is over, Roxas will immediately RTC in Mission Mode. There is an optional Invisible to face in the Secret Depths area. Jump up to the highest platform and it will appear. It is extremely weak against Fire magic, but Thunder magic will cure the Heartless.

Challenge Mission
Magic is the key here to exploit the elemental weaknesses of the Heartless you will face to bring them down quickly. Equip either Darker Than Dark+ or Crown of Guilt++ along with whatever magic units you have and equipping a ring to raise the Magic Stat can also help. For magic, stock up on Blizzard, Thundaga, and Aero particularly at LV5 along with a few Cura casts, and some Elixirs for restoring magic casts. It is also a good idea to equip Haste, High Jump, Air Slide, and Glide at the highest level you can to help with moving through quickly. Once started, head straight for the Secret Depths, ignoring the enemies in the Entrance Hall. At the Secret Depths, lock on and use Blizzard to take down the Scarlet Tango as it can do multiple hits against them, and defeat Aerial Master with Thundaga. Make sure to know where these Heartless appear if you need to help save time. At the Lamp Chamber, quickly defeat the two Scarlet Tango with Blizzard, and then engage the Land Armor by locking on and carefully strike it in the air with Aero, then keep using Aero to defeat it. A few problems here are the uneven floor in the Lamp Chamber which would make it difficult to attack Land Armor when it is down, so predict how far in the air you should be when you fire Aero if it becomes a problem and staying a good distance away from Land Armor due to its vicious counterattack when it recovers. It won't be too hard to get 3 Challenge Sigils by using this strategy.