The Ghosts of Bern

The Ghost of Bern is the chapter 23 of Fire Emblem: Sword of Seals. This Chapter can only be accessed if the player had all the legendary weapons at the end of The Neverending Dream. This chapter can be a bit hard, since there are alot of enemies everywhere, some Druid with Sleep Staff near Brunya who is the boss of this chapter. Be sure to bring strong, fast units with high HP and defense, so that they can kill the enemies here. At first some wyverns will storm you from the north, while the archers in the little isle in the middle of the lake will attack you with the ballistae. Brenya is guarding the temple where the dark dragon is.

From where you start, if you visit the village with fir, karel will join you in lvl 19 and all of his growths are above 100% so if he gets a level up it will always be a perfect level up.