Simple
Doubles the Pokémon's stat modifiers. These doubled modifiers are still capped at -6 or 6 stages.
Full effect
Each stage of this Pokémon's stat modifiers acts as two stages. These doubled stages are still limited to a minimum of -6 and a maximum of 6. This Pokémon can still accumulate less than -3 or more than 3 stages of stat modifiers, even though the extra ones have no effect after doubling.
In-game description
Doubles the effects of the Pokémon's stat changes.
Stats
Regular ability (3 Pokémon)
Hidden ability (2 Pokémon)
Only available through specific encounters (Dynamax Adventures, Tera Raids, hidden grottoes, etc.).