When a stat of a Pokémon with this Ability is lowered by an opponent, its Attack is increased by two stages. Defiant will not activate if the Pokémon with this Ability lowers its own stats (such as with Close Combat) or if its stats are lowered by an ally.
If multiple stats are lowered (such as by Memento or Venom Drench), Defiant activates for each stat lowered.
If the Pokémon with this Ability is holding a White Herb, if a stat other than Attack is lowered, Defiant will trigger before the White Herb, so the user will receive the Attack boost and then the lowered stat will be restored. If its Attack is lowered, Defiant will activate first, increasing its Attack so that the White Herb cannot activate.