Expotential Growth

Only {g} can be used to cast this spell.
You may search your library for any number of
forest lands and put them onto the battlefield
tapped, then shuffle your library.
Until your next turn green creatures you control
gain +1/+1 and trample.
"Hey that forest wasn't there yesterday, and neither
was that one, or that one! What's going on here?"
~Weary Traveler.