Defiant
Raises Attack two stages upon having any stat lowered.
Full effect
When any of this Pokémon's stats are lowered, its Attack rises by two stages. If multiple stats are lowered at once, this ability takes effect with each stat lowered.
In game description
If the Pokémon has any stat lowered by an opposing Pokémon, its Attack stat will be boosted sharply.
Pokemon with Defiant
#0056
Mankey
hidden
#0057
Primeape
hidden
#0083
Farfetchd
hidden
#0432
Purugly
hidden
#0624
Pawniard
#0625
Bisharp
#0628
Braviary
hidden
#0641
Tornadus Incarnate
hidden
#0642
Thundurus Incarnate
hidden
#0766
Passimian
hidden
#0862
Obstagoon
hidden
#0870
Falinks
hidden
#0979
Annihilape
hidden
#0983
Kingambit
#1017
Ogerpon
Mankey
hidden
#0057
Primeape
hidden
#0083
Farfetchd
hidden
#0432
Purugly
hidden
#0624
Pawniard
#0625
Bisharp
#0628
Braviary
hidden
#0641
Tornadus Incarnate
hidden
#0642
Thundurus Incarnate
hidden
#0766
Passimian
hidden
#0862
Obstagoon
hidden
#0870
Falinks
hidden
#0979
Annihilape
hidden
#0983
Kingambit
#1017
Ogerpon
Using Defiant in Cobblemon
Abilities are passive and always active, so Defiant 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.