From Bulbapedia, the community-driven Pokémon encyclopedia.
Extra Rule cards (Japanese: おすすめルール Suggested Rule) are a classification of trading cards in Japan only released in the third series of Vending Machine cards. They have no rarity and all of the illustrations were done by Nobuyuki Habu.
Extra Rule cards alter the way the game is played by providing an additional rule. In most cases these rules can only be enacted before beginning play, so they cannot be played during the game.