Nightmarish

Nightmarish is a Boss Modifier found on Champions, Bosses, and their minions in Diablo III. When a boss with this ability hits your hero or pet, there is a percent chance that that target will be inflicted with the Horrify effect and will turn and run away from the inflicting monster.

There is no added damage or any other debuff from the attack; the danger comes from a loss of control of your character, and the possibility that they will run into something very dangerous; a cluster of enemies, or another damaging boss effect, such as Molten, Arcane Enchanted, Plagued, etc.

A Monk running scared.

The Patch 1.0.4 nerfed this ability slightly, providing frightened targets with 6 seconds of immunity to being frightened again after each incidence. This prevents characters, pets, or minions from being feared and re-feared in rapid succession.[1]

Nightmarish

• Monster Level Minimum: 2
• Available to: Champions, Bosses, and Boss minions.
• Damage Type: N/A.
• Additional Resistances: None.
• Can Not Spawn With: Vortex or Knockback.

Strategy

The only way to avoid the Nightmarish effect is not to get hit by bosses with that property. This can be tricky, though various defensive skills can negate or counter the fear effect. It was much more vexing shortly after release when the effect could be repeatedly inflicted; ranged attackers were especially difficult as melee characters could keep getting feared while trying to close into range.

The real danger of Nightmarish is when enemies are nearby when it hits, rendering your character helpless -- unable to attack or use any skills -- for the duration. This can be deadly against hard hitting melee attackers, especially when dangerous AoE boss effects are in the vicinity.

Players or pets feared who have nowhere to run due to obstacles such as Jailer or Waller, terrain obstacles, or just a wall of monsters, will stand still until the fear wears off, potentially taking damage the entire time.

Media

The Nightmarish effect is marked by a small screaming skull over the target's head, exactly as inflicted by the Witch Doctor's Horrify skill. There is no visual indication on the boss that they have the ability, other than in their tooltip hover text.

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  Skeleton boss pack.

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  Barbarian runs.