Rivalry
Increases damage inflicted to 1.25× against Pokémon of the same gender, but decreases damage to 0.75× against the opposite gender.
Full effect
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.
In-game description
The Pokémon's competitive spirit makes it deal more damage to Pokémon of the same gender, but less damage to Pokémon of the opposite gender.
Stats
Regular ability (13 Pokémon)
Hidden ability (4 Pokémon)
Only available through specific encounters (Dynamax Adventures, Tera Raids, hidden grottoes, etc.).