Curse is an offensive Ghost-type move. It works differently for Ghost-type Pokémon than those of other types.
The user will lose half of its maximum HP (rounded down) and put a curse on the target. If the user has less than half of its maximum HP remaining, the move will execute fully but cause the user to faint. A cursed Pokémon will lose ¼ of its maximum HP at the end of each turn. The curse will remain until the Pokémon switches out or the battle ends. This move is not blocked by Protect, Detect or Spiky Shield, but is blocked by Crafty Shield.
The user does not lose HP if Curse misses (due to a move with a semi-invulnerable turn), fails (due to the target already being affected by Curse), or is blocked by Crafty Shield.
The user's Speed stat will drop by one stage and its Attack stat and Defense stat will rise by one stage each. Despite being an effect acting on the user, this move will fail if there are no opponents on the field.