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The user faints. The target's Attack and Special Attack are lowered by two stages. The user faints unless this move misses or there is no target. If the opponent uses Protect or Detect, or has a Substitute up, it has no effect, but the user still faints. Does not fail if the target's stats cannot be altered.
Memento can provide an opportunity for the user's teammate to use a stat-boosting move, as the opponent will likely be unable to KO it due to the Attack and Special Attack drops. Using Reflect and Light Screen before Memento makes set-up even easier. Memento is also an effective weapon against Baton Pass teams that focus on passing Shell Smash, as the boosts to Attack and Special Attack will be nullified.
Healing Wish is a similar move that faints the user but fully restores the HP and status of a teammate.
Lunar Dance is a similar move that faints the user but fully restores the HP and PP of a teammate and its moves.