REF: https://callmepartario.github.io/og-dhsrd/#adversary-benchmarks-type-minion

Since minions don’t have damage dice, a critical success on an attack roll doesn’t increase damage. The GM might decide a minion (or Group Attack) doubles the damage instead

Minions are easily dispatched, but dangerous in numbers. The Minion feature determines how many additional Minions are defeated by incoming damage. Minions don’t make damage rolls, and use a flat damage modifier instead. Add the Group Attack feature, using the same damage dealt by the basic attack. Don’t assign too many other adversary features.

Minion (X)—Passive: The Minion is defeated when they take any damage. For every X damage a PC deals to the Minion, defeat an additional Minion within range the attack would succeed against.

Group Attack—Action: Spend a Fear to choose a target and spotlight all adveraries with the same name 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 Y physical damage each. Combine this damage.