Justified
Raises Attack one stage upon taking damage from a Dark move.
Full effect
Whenever a Dark-type move hits this Pokémon, its Attack rises one stage. The move is not negated in any way.
In game description
When the Pokémon is hit by a Dark-type attack, its Attack stat is boosted by its sense of justice.
Pokemon with Justified
Using Justified in Cobblemon
Abilities are passive and always active, so Justified costs you nothing to run. If it is marked hidden on a species above, expect it to be harder to obtain: servers differ in whether hidden abilities come from breeding, an Ability Patch, or events.
See the Pokedex for which abilities each species can have, and IVs, EVs and breeding for how to actually pass one down.