As an additional cost to cast this spell, sacrifice a green creature.
Search your library for a green creature card and put it onto the battlefield. Then shuffle your library.
6/8/2016 Sacrificing a green creature is part of Natural Order’s cost. You can’t sacrifice more creatures to search for more creature cards, and you can’t cast Natural Order at all if you control no green creatures.
6/8/2016 Players can respond to this spell only after it’s been cast and all its costs have been paid. No one can try to destroy the creature you sacrificed to stop you from casting this spell or to make you sacrifice a different one.