Simple

When one of this Pokemon's stat stages is raised or lowered, the amount is doubled.

5 Pokémon have this ability

#322

Numel

FuegoTierraHoenn

#399

Bidoof

NormalSinnoh

#400

Bibarel

NormalAguaSinnoh

#527

Woobat

PsíquicoVoladorUnova

#528

Swoobat

PsíquicoVoladorUnova