In battle
Intimidate lowers the opponent's Attack stat by one stage upon entering the battle. It is triggered both when a battle begins and when a Pokémon with Intimidate switches into battle. It affects all opponents in Double Battles but will only affect adjacent opponents in Triple Battles.
In Generations III and IV, Intimidate's activation message reads: "[Pokémon]'s Intimidate cuts [opponent]'s attack!". In Generation V, the message changed to "[opponent]'s Attack fell!".
Intimidate has no effect on Pokémon who are immune to Attack stat reductions, such as Pokémon with Clear Body, Hyper Cutter, or White Smoke. This Ability will not affect a target with a substitute.
In Mystery Dungeon, Pokémon attacking a Pokémon with this Ability with a physical attack will have a 20% attack penalty.
Outside of battle
From Pokémon Emerald onwards, if a Pokémon with Intimidate is leading the party, Intimidate decreases the chance of encountering a lower-level wild Pokémon by 50%. It shares this effect with Keen Eye.