Natural Order

As an additional cost to cast this spell, sacrifice a green creature.
Search your library for a green creature card, put it onto the battlefield, then shuffle.

Mystery Booster 2

"Nature is neither cruel nor kind. It operates on necessity, not sentiment."
—Dina, Witherbloom mage-student

Strixhaven Mystical Archive

「自然は残酷でも親切でもない。感情ではなく、必要性に応じて機能するのよ。」
――ウィザーブルームの魔道生徒、ダイナ

. . . but the price of Mangara's freedom was Asmira's life.

Eternal Masters

As an additional cost to cast Natural Order, sacrifice a green creature.
Search your library for a green creature card and put it onto the battlefield. Then shuffle your library.

Magic Online Promos

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.

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.