Alistair, Errant Archaeologist

Defender

{t} Excavate {x}(Sacrifice a land card. Exile cards from the top of your library until you exile an Artifact spell with mana value of {x}. Cast it without paying its mana cost or put it in your hand. Put the rest on the bottom of your library in a random order)

When this card would be destroyed, pay {3}{p/c}{p/c} and exile it instead. Return it to the battlefield transformed.