Serpentine of Wakatu Sea

{u}Ttarget player puts 1 card on top of their library into their graveyard.
{w}You gain 1 life
{u}{u}{w}{w}You draw a card and gain 2 life
{t}{u}{u}{u}{w}{w}{w} Sacrifice Serpentine of Wakatu Sea. You gain 5 life, draw 3 cards, and if you have 50 or more life, destroy all target player's creatures.