Whenever Risen Reef or another Elemental you control enters, look at the top card of your library. If it’s a land card, you may put it onto the battlefield tapped. If you don’t put the card onto the battlefield, put it into your hand.
"No, not 'washed' ashore. It *walked* ashore."
—Shafring Hulm, beachcomber
If you put the card into your hand, you don’t have to reveal it. You also don’t have to tell your opponent whether it’s a nonland card or a land card you decided not to put onto the battlefield tapped.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.