The Thrall is defeated when they take any damage. For every 13 damage a PC deals to the Thrall, defeat an additional Minion within range the attack would succeed against.

Spend a Fear to choose a target and spotlight all Outer Realm Thralls within Close range of them. Those Minions move into Melee range of the target and make one shared attack roll. On a success, they deal 11 physical damage each. Combine this damage.