I have never played Shadow and Flame the scenario myself, but have seen the spoiled DB card, how do you attack DB with heros/allies, since he is in the staging area and never leave it ?You can't attack in staging area except Dunhere and a few event cards which allows you to attack.

Durin's Bane
Type: Enemy
Encounter Set: Shadow and Flame
Threat Threashold: 1
Threat: 4 Attack: 6 Defense: 3 Hit Points: 27
Balrog. Flame. Shadow.
Regenerate 3. Indestructible. Players cannot play attachments on Durin's Bane.

Durin's Bane cannot leave the staging area, is considered to be engaged with each player whose threat is 1 or greater,
and attacks each of those players in turn during the combat phase (deal and discard a new shadow card each attack).

He is considered engaged with each player with threat > 1, so you can attack him normally, use Feint on him, etc… However, he is immune to effects that would remove it from play and effects that would return him to the staging area have no utility there.