Chapter 9: A Grim Reunion
Chapter's objective: Seize the castle's door.
Note: This is a foggy map, this is not shown on the image for you to see everything on it.
You will encounter a lot of enemies on this map and the best strategy is to stay together and defend against them on the bridge area until the attacks end. On the actual bridge you should place Wallace, that way nothing will go through and he will leave most enemies with very few HP so you can place Wil as a backup to kill weakened units and gain a few levels in the process. You should also control the enemies coming from the south fortress, to do so you should place Lucius and Nils there to kill the brigands before they get to the plains, the reason to use Nils here is because enemies on peaks get a big avoid bonus, so Lucius may fail an attack and Nils would give him another chance it that happens (you can also place Lyn on the forest closest to the mountains and wait for the brigands there). You should also be aware of the enemies coming from the northern path, lance wielding soldiers and a few brigands that Sain and Kent shouldn't have any problems against.
Once you notice that no more enemies are coming, you can assume it is safe for you to move to the castle and kill the boss. Best units against this paladin are Lyn and Wallace, Wallace won’t make as much damage but it will resist the boss’ attacks; Lyn, on the other hand, will make the most damage against him with her Mani Katti but she will also receive more damage so you should be careful.