Leyline of Torrential Downpour

If Leyline of Torrential Downpour is in your opening hand, you may being the game with
it on the battlefield.
If an opponent would mill one or more cards,
he or she mills an additional two cards.
{3}{u}: Target opponent mills three cards. Activate this ability only as a sorcery.
"When it rains it pours." —Ashiok, Dream Render