Fire Emblem: Path of Radiance Playthrough Part 14
7In this video, we complete "Chapter 27: Moment of Fate" and "Chapter 28: Twisted Tower!
Chapter 27 is very, VERY important. The Black Knight fight is unique, and how you approach it will slightly affect the story's progression.
If you manage to defeat the Black Knight, you'll get Nasir as a unit and rescue both him and Ena from being crushed by the collapsing castle. If you don't defeat him within the turn limit, Nasir traps the Black Knight, but the castle collapses on both of them. Afterwards, Ena joins you.
The Black Knight fight for the most part boils down to just luck. Now that you have access to Ragnell, you're actually able to damage him. You can only use Ike and Mist during this part, so you want to be really careful, especially if Mist is underleveled. If she has Physic or she's promoted to a Valkyrie, good! You'll have a much easier time.
What you want to do is immediately rush the Black Knight with Ragnell equipped and attack him. As I said earlier, it's really just luck. Just hope that you activate Aether a lot and that the Black Knight hardly activates Luna. If Ike can't take another hit from the Black Knight, heal him up with Mist and get her out of the way. The reinforcements that come up will actively try to go after Mist, which is why I think Physic helps out a lot here.