This section is incomplete. Please feel free to edit this section to add missing information and complete it. Reason: Can a Pokémon that gained a Hidden Ability this way pass its Hidden Ability down via breeding?
If used from the Bag, it changes a Pokémon's Ability from one of its standard Abilities to its Hidden Ability. It cannot be used to change a Pokémon's Ability from its Hidden Ability to one of its standard Abilities.
The Ability Patch can only be used on a Pokémon that belongs to a species that has a Hidden Ability. For example, it can be used to change a Rookidee's Ability from Keen Eye or Unnerve to Big Pecks, but it cannot be used to change a Metapod's Ability (which is always Shed Skin).