Yggdrasil, Tree of Realms

Hideaway (This card 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.)
{t}: Add {c}{c}.
{1}{c}, {t}: You may play the exiled card without
paying its mana cost if a library has twenty or
fewer cards in it.