Winning a game by removing all of the cards in your opponent’s library is a strategy that appears in every format and can be effective at times. Winning via this method or causing cards to go from a library to a graveyard is called milling. This name comes from one of the first cards to do this, Millstone. Other more recent cards that help with this method are; Jace’s Erasure, Merfolk Mesmerist and the last portion of Decimator Web‘s ability.

The important rules aspect of winning via this method is that players do not lose the game when their library is empty. Players only lose the game when they can no longer draw cards due to the fact that their library is empty. So, if your opponent only has four cards in his library and you remove all of them with Tomb Scour, you will not win yet. It does not matter that Tomb Scour had him remove more cards than were there. None of them were drawn, so he will not lose. Your opponent will most likely lose at the beginning of his next turn when he is instructed to draw a card.