Jirachi

Once during your turn (before your attack), if this Pokémon is your Active Pokémon, you may look at the top 5 cards of your deck, reveal a Trainer card you find there, and put it into your hand. Then, shuffle the other cards back into your deck, and this Pokémon is now Asleep.

It is said to have the ability to grant any wish for just one week every thousand years.