Forest River Cave

When Forest River Cave enters the battlefield,
you may search your library for an artifact with a converted mana cost of X or less, put it onto the battlefield tapped, then shuffle your library.
{t}: Add {g} or {u} to your mana pool.
{g/u}{g/u}{g/u}{g/u}, {t}: Gain control of target artifact
until its controller pays that artifact's converted
mana cost in life.