The Scenario Power known as "Necromancer Damage" (at least as it says in the moment the damage is dealt) isn't working properly. The description says that it should deal 1d4 cold damage when a character defeats a henchman (what is quite vague, since the damage fortunately only occurs once, after the second damage was defeated), but as I could see, the animation was that of a force damage (similar to Nualia's initial attack), that I could confirm after a Hide Armor of Acid Resistance (that also resists cold) did not gave an option to recharge. And instead of 1d4 damage, the power deals 1d6 damage.
In short, the power says "When a henchman is defeated, each character is dealt 1d4 cold damage", but probably works like "When the second henchman is defeated, each character is dealt 1d6 force damage".