Mission 49: Collect hearts

Mission 49 in Kingdom Hearts 358/2 Days is an optional mission where Roxas heads back to Beast's Castle with Xigbar for a round of heart collection.

Accessing the Mission
This mission becomes available after scoring 50 or more points in the Grandstander minigame during Mission 37: Vacation and speaking to Luxord in the Grey Area between Day 153 and Day 155.

If the mission is not unlocked at this time, it will still become available as a Holo-Mission along with Missions 45-48.

Mission Goal
Collect hearts.

Mission Walkthrough
As with all heart collection missions, the Mission Gauge advances every time you defeat an Emblem Heartless, reaching 100% completion when every Heartless is defeated. Thorough exploration is the key to full completion.

Bring along as many casts of magic as possible, especially Fire to take out the Icy Cubes and Snowy Crystals. Blizzard and Aero magic will be helpful against the Snapper Dogs and Bully Dogs you will encounter. Also take Ethers and Hi-Ethers to extend your casting ability.

The first Heartless are located near the center of the Entrance Hall, just southwest of the starting point. From there, exit south to the Courtyard, where the next Heartless can be found in the center. After defeating those, exit south to the Bridge, where you can find the next group of Heartless and a chest. Return to the Courtyard when you're finished.

From the Courtyard, head for the Entrance Hall Upper Level by way of the secret passage to the left of the stairs. Fully explore the area to find four groups of Heartless to defeat. Afterwards, take the northmost exit to the upper level of the Ballroom, where you can find the Unity Badge. Descend to the main floor to find another group of Heartless in the center of the floor, as well as a Cymbal Monkey in a chest near the middle of the room.

After clearing the Ballroom, return to the Entrance Hall, and then head to the East Wing. Here you will find another group of Heartless and a chest. Return to the Entrance Hall, and go to the West Hall. Defeat the next Heartless along the way towards the north. Enter the Undercroft through the northwest door, and defeat the large group of Icy Cubes in the center of the floor. Afterwards, continue into the Secret Passage, where there are four groupings of Heartless to defeat.

Upon exiting the Secret Passage, head to the West Wing to find the final Heartless in the mission. Once you are finished, collect all remaining chests and RTC.

Video
Video walkthrough here.