MAGIC: THE GATHERING
: Add to your mana pool.
: Draw a card. Activate this ability only if you have exactly seven cards in your hand.
Library of Alexandria is a draw engine that is very difficult to interact with. In control mirrors it's usually game over if it is in your opening hand, especially if you are on the draw, since you can play the land and immediately activate it. Library of Alexandria is a staple of Blue Vintage decks and is so good that it is restricted in the very powerful format.