Fire Emblem 7: Sonia

Not to be confused with Sonya. Or Sonja. The map's layout and gimmick can make it difficult to approach before she runs out of Bolting and Fimbulvetr hits harder than Elfire. Still, at this point in the game you should be more than equipped to deal with her. Try throwing Jaffar at her and getting a Lethality proc for some fireworks. Stick around after the boss to see the Sonia/Nino boss conversation.