Suggested by Nsl98
No, Link is not fighting them all at once. It will be a gauntlet style match, with Link in his Hyrule Warriors incarnation. All the members will be fought in the areas you fight them in Kingdom Hearts. In the case of Xemnas, it will only be his first form.
1. Demyx (Castle Gate, Radiant Garden)
2. Vexen (Twilight Town Mansion)
3. Xaldin (Beast’s Castle, Bridge)
4. Lexaeus (Castle Oblivion)
5. Zexion (Destiny Islands)
6. Luxord (Castle That Never Was Ramparts)
7. Larxene (Castle Oblivion)
8. Saix (Castle That Never Was Tower)
9. Xigbar(Castle That Never Was, Hall of Empty Melodies)
10. Axel (Twilight Town Sandlot)
11. Marluxia (Castle Oblivion)
12. Xemnas (Memory Skyscraper)
13. Roxas (Station of Serenity)
Does he clear it?
Or will Link get turned into a Dusk?