Land Hideaway (This land enters the battlefield tapped. When it does, look at the top four cards of your library, exile one face down, then put the rest on the bottom of your library.)
Rare
{T}: Add {U} to your mana pool.
{U}, {T}: You may play the exiled card without paying its mana cost if a library has twenty or fewer cards in it.
Illus. Mark Tedin

10/1/2007: It doesn't matter which library has twenty or fewer cards in it, and you don't have to specify a library.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern