Whispering Bluffs

This land enters the battlefield tapped. When it does, exile the top five cards of your library face down under Whispering Bluffs. At any time, you can look at the cards exiled this way.
{t}: Add {c} to your mana pool.
{4}, {t}: Exile a creature you control, you may put another creature card exiled with Whispering Bluffs into play under you control.