Gaia, Mother of All

Indestructible
{t} Add three mana of either {g}, {r}, or {u}.
{t} Pay {x}{g} then search for X lands in your
deck that produces the mana in the mana cost of
this card, place them on the board.
As long Gaia, Mother of All is on the board lands
can't be destroyed and you can choose to replace
a land you control on the board with a land in
your hand at any time.