Strategies for Normal/Hard
This is a pretty straightforward chapter, you simply have to move north and defeat Marth. What may make it difficult is the fact you can only bring Chrom and 5 other members. You may want to pair compatible units together in order to maximize potential, or move all units to one side to handle one side at a time rather than dealing with both sides as you move upward.
The boss himself isn’t too difficult to deal with. If you bring Lissa on the level as a healer, just be sure to keep her out of enemy ranges as per usual.
Strategies for Lunatic
Enemies come in swarms, the first two, then the second two, etc. Frederick should try and take out the mages when possible; keep enemy ranges open so he can outrun and heal when needed. Using the stairways is always a plus.