Forest's Curse (move)

Effect

 * Forest's Curse adds the Grass type to the target, in addition to the Pokémon's original type(s).
 * If it is used against a dual-type Pokémon, that Pokémon will have three types at once. If the target already has an additional type added to it by Trick-or-Treat, that type is replaced with the Grass type. Forest's Curse will fail if the target is already Grass-type.