Do you have defeated The Black Serpent scenario in solo?
I'm playing in solo the Harad cicle with my 3 Hunters deck (Aragorn lore, Gimli leadership, Legolas spirit).
I've defeated all the quests until Beneath the Sands with this deck (also the pod The Siege of Annuminas!), but this scenario is terribile in solo.
What is your deck used to win against it?
It is hard, official rating 8.