Rivalry in Pokémon Brilliant Diamond & Shining Pearl

Increases damage inflicted to 1.25× against Pokémon of the same gender, but decreases damage to 0.75× against the opposite gender.

This Pokémon inflicts 1.25× as much regular damage against Pokémon of the same gender and 0.75× as much regular damage against Pokémon of the opposite gender. If either Pokémon is genderless, damage is unaffected.