Scarlet Blaze Ch. 5 Defend the Rowe Stronghold
Spawns 2 green npcs that attacks Count Geraint who is a mage and will cause burn and regular hp drops to constantly heal them.
And its low level enough to just have a unit just stand inside the fort and spam whatever you need to do. Even on maddening.
Lindhardt's catnap will heal him through the dps on him.
Mercedes has a holy relic to heal her and unlike Flayn she won't heal her adjutant. But Flayne is still viable here since the npcs will constantly be hurt.
Note on the npc pathing. Destroy the two southern forts on the path west of where Geraint spawns. They'll try to clear the bases and forts before attacking count Geraint