Nightmare is a Ghost-type status move with no power or accuracy check, as it only works if the target is already asleep. Once Nightmare is successfully applied, the affected Pokémon will lose 25% of its maximum HP at the end of each turn until it wakes up. Introduced in Generation II, Nightmare provides a strategic way to continuously damage and pressure opponents, especially when combined with sleep-inducing moves like Hypnosis or Spore. This move is particularly notable for its use in setting up end-turn damage over a prolonged period, making it a useful tool in stall and status-centric strategies. However, its utility is limited to situations where the target can be reliably put to sleep.