Rivalry
18 Pokémon can have Rivalry: 14 as a regular Ability and 4 as a Hidden Ability.
What does Rivalry do?
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.
Which Pokémon have Rivalry? (14)
Which Pokémon have Rivalry as a Hidden Ability? (4)
How Abilities work · Hidden Abilities explained · Every Ability