Shelldock Isle [Lorwyn]

Hideaway 4 (When this land enters the battlefield, look at the top four cards of your library, exile one face down, then put the rest on the bottom in a random order.)
Shelldock Isle enters the tapped battlefield.
{T}: Add {U}.
{U}, {T}: You can play the exiled card without paying its mana cost if a library has twenty or fewer cards in it.