Nightmarish

From Arkham Horror Wiki

Nightmarish is a monster special ability.^[1]

Nightmarish X: Any investigator that passes a Horror check when facing this monster still loses X Sanity. This ability doesn’t apply if the investigator fails the Horror check.

Example: A Dark Young (Nightmarish 1) causes an investigator to lose 3 Sanity if the investigator fails his Horror check or 1 Sanity if the investigator passes. The Sanity loss from Nightmarish 1 doesn’t apply if the investigator has already failed the Horror check.

References