You may have up to 4 Basic Pokémon cards in your deck with Unown in their names.

Whenever 1 of your Pokémon with Unown in it's name uses its Hidden Power attack, that attack does 10 more damage for each damage counter on Unown [A]. If you have more than 1 Unown [A] in play, use only 1 [Anger] for each attack.