After escaping an attack at sea, you reach the leisure city of Cyrkensia.
Have Corrin Escape
The objective is to send Corrin to the red tile in the middle of the north edge of the map. This is actually very easy to do. Just pair Corrin up with a flying unit, fly to the escape tile, separate, and have Corrin use the escape tile.
However, if you battle some enemies, you can get a Dracoshield, Hammer, and 3000 G.
A Great Knight in the southeast of the map is carrying the Hammer, so kill that unit to get the Hammer.
The Dracoshield is in a chest, but an enemy Outlaw will grab it. You can just kill that Outlaw to get the Dracoshield.
The Outlaw in the southeast of the map is carrying the 3000 G.
There is a Dragon Vein in the southeast of the map that will freeze the water, allowing all walking units to walk across. This will make things more difficult for you because the enemy units will easily be able to surround you. I don't recommend using the Dragon Vein.
After several turns, Xander and his two retainers show up. Xander is impossible to defeat at this point, so if you do intend to kill the enemy units before having Corrin escape, don't bother attacking Xander. Just ignore him and escape when he is the last enemy unit left.