Moses, Splitter of Seas

{t}, Sacrifice an Island you control: Reveal the top 4
cards of your library and split them into 2 piles.
Target opponent chooses a pile, you may put the
other into your hand. If the chosen pile contained
a land, deal X damage to the chosen opponent,
where X is the number of islands you control. You
may put a land card from your hand onto the battlefield.