Mission 43: Eliminate the giant Heartless

Mission 43 in Kingdom Hearts 358/2 Days is a mission at Beast's Castle that finds Roxas and Xaldin hunting down two nasty Heartless.

Regular mission
Eliminate the giant Heartless.

Story summary
Roxas helps Xaldin to destroy two Heartless threatening the Beast and those in his castle. While there, Xaldin decides to investigate the Beast further and delightedly learns about the spell surrounding his rose. Later, Roxas and Axel discuss the nature of being Nobodies and the memory of emotions.

Mission walkthrough
You will enter in the Courtyard. Hope you like Pureblood Heartless, because there will be a ton of them on this mission, including two groups in the center and on the eastern side of the Courtyard. The main door to the castle is sealed off, so you will have to enter the castle through the secret passage into the Entrance Hall Upper Level. Still more Heartless line the way, but you will want to head towards the door to the Ballroom in the center of the northern curved section.

Jump down into the Ballroom proper. Nothing here yet, so try to head through the bottom doors into the Entrance Hall. Oh wait, there they are! Possessors, Shadows, and a Gigas Shadow pop up behind you. The Possessors and Shadows do not respawn, so feel free to take them out if they are in your way. Continue as you were, into the Entrance Hall.

There's nothing in the Entrance Hall but more Shadows and a Unity Badge, so after collecting your spoils, head up the stairs to the East Wing to collect another of the chests. There are some Mega-Shadows, but nothing difficult, so if you already have the chest, there's really no reason to go there. Backtrack to the Entrance Hall, then head up the stairs to the West Hall.

Upon entering the West Hall, you'll be hit with a massive number of respawning minor darkness. With Xaldin's help, this shouldn't be terribly difficult, but keep an eye on your health all the same. Once you've taken them all out, head for the north end of the hall, and your goal presents itself: the Dark Follower, who looks a lot like Darkside's cousin, and acts a lot like him, too. Take him out, and you'll automatically RTC after the cutscene.