(Does not move)
Strategies for Normal/Hard
This is the first map you can choose to bring who you want. You have to bring Chrom no matter what. There is room for eight including him, so you will have to leave one unit back at base as a minimum.
When you begin, there will be a cutscene, and Sumia will then join your team. Now when you are able to move, be sure to recruit Kellam, to your left. You must speak to him with Chrom in order to recruit him. He is a fairly useful Knight! He should be in Chrom’s range right at the start of the turn.
There are quite a few Archers if playing on Hard mode or above, so be sure to take extra care in keeping Sumia out of trouble, as they are extra effective against her. Be sure to keep their ranges highlighted or in mind.
You can either split your team into two, or proceed one way (either left or right), kill the enemies with the door keys, and then proceed up past the door and reunite at the top. For more experience, you can always take your time and wipe out the rest of the units. If in a hurry though, one way will be much quicker.
If you manage to defeat the Fighter who drops a Hammer, that will help greatly against the boss, as it is extra effective against armored foes. You can also use Chrom’s Rapier if he still has it too.
Strategies for Lunatic
You will want to get Chrom to Kellam, recruit him, pair up, and quickly run back out of enemy range. Then use Frederick as a lure and hope that he can wipe out most enemies that attack him.
Though the archers may cause a little trouble. Take them out the next turn if possible; Frederick should be able to kill one (pending on his stats and who he’s paired up with), and use the rest of your units to kill the other.
Now you’ll have to deal with the right side, I advise hiding the other units and healing Frederick up, and sending him against the right side.
If you manage to survive this far, then you can use either the left or right (I recommend left) door as a chokepoint, and let the enemies come to Frederick. Beware of the enemy with the Hammer! Aside from him, the rest of the level should be straightforward.