Fear Incarnate

One stack gives 10% increased Culling Strike Threshold. The buff can reach 20 stacks for 200% increased threshold, and gaining another stack refreshes the 10-second duration. At maximum stacks, the base 5% Unique-enemy threshold becomes 15%, the 10% Rare threshold becomes 30%, and the 20% Magic threshold becomes 60%. Horror's Flight grants one stack whenever you Cull a target, whether the cull comes from its Crushing Fear skill or another culling effect used by you.

Each stack gives 10% increased threshold

Fear Incarnate modifies the Culling Strike threshold, not the damage of the culling Hit. Its increased value scales the base threshold for the target's rarity.

The base threshold depends on enemy rarity

Culling Strike checks Normal enemies at 35% Life, Magic enemies at 20%, Rare enemies at 10%, and Unique enemies at 5%. The check occurs before the Hit deals damage.

The stack formula is base threshold times the total increase

With only Fear Incarnate, use base threshold multiplied by 1 plus 0.10 per stack. Five stacks give 50% increased threshold, ten give 100%, and twenty give 200%. Other increased Culling Strike Threshold modifiers add to the same total increase.

Gaining a stack refreshes the whole 10-second duration

Fear Incarnate does not track a separate expiry timer for each displayed stack. Gaining another stack refreshes the buff duration, letting repeated culls maintain and build the stack count.

The maximum is 20 stacks

At 20 stacks the buff supplies 200% increased Culling Strike Threshold. Further qualifying culls refresh the duration but cannot raise the count above 20.

Horror's Flight is the source

The Unique Engraved Bracers grant Crushing Fear and the modifier Gain 1 Fear Incarnate when you Cull a target. The wording is not limited to Crushing Fear, so another culling effect used by you can generate a stack.

Crushing Fear is the built-in culling skill

Crushing Fear is a Quarterstaff Strike that dashes to a target, cannot be evaded, converts part of its Physical damage to Chaos, and has Culling Strike. When it kills an enemy, it creates a much stronger shockwave whose damage and area scale with the killed target's Power.

Way of the Stonefist replaces the stack effect

When Horror's Flight is transformed into Fists of Stone by the Martial Artist's Way of the Stonefist, its cull modifier grants Fear Overwhelming instead. Each Fear Overwhelming gives 5% increased Area of Effect for Attack Skills for 10 seconds, up to 20 stacks.

Runic Ward prevents culling

A monster cannot be Culled while it has Runic Ward. Because Horror's Flight requires you to Cull a target, no Fear Incarnate stack is generated until the target can actually be culled.