Gailualen, the Ebb and Flow

Lifelink, vigilance
Gailualen's toughness is equal to your life total.
Whenever you gain life, look at the top card of
any player's library. You may choose to put that card on the top or bottom of that library, or put that card on top and shuffle that player's library. Then, if you gained 5 or more life this turn, draw a card.