Challenge 2 Hard should be fairly simple with Azura and Reinhardt. Since the enemies are in groups of 2, you can have Reinhardt kill one, then have Azura Sing to let him kill the other. Letting Azura or Subaki simply tank the enemy units with their Sapphire Lances works, too. Challenge 5 Hard I'm not entirely sure of enemy stats (so no idea if this will actually work, someone else might have to confirm since I'm out of stamina myself). Assuming your Klein can one-round kill the enemy Klein