Generation Vii
Beast Boost
The Pokémon boosts its most proficient stat each time it knocks out a Pokémon.
Detailed Effect
Raises this Pokémon's highest stat by one stage when it faints another Pokémon.
Pokémon With Beast Boost
11 canonical Pokémon forms can have this Ability.

Nihilego
Buzzwole 
Pheromosa
Xurkitree 
Celesteela
Kartana
Guzzlord
Poipole
Naganadel
Stakataka
Blacephalon