A spare green creature can become the largest threat in your library with Natural Order. Four mana and a sacrificed creature let you search directly for a green creature and put it onto the battlefield. There is no mana-value ceiling, so a modest mana Elf can turn into Craterhoof Behemoth, Terastodon, or another creature built to change the board immediately.
Creature-heavy green decks make the best use of the exchange. Craterhoof rewards a board that already has several attackers, while Terastodon can remove troublesome noncreature permanents. Protean Hulk offers a different direction, setting up a later death trigger and a package of smaller creatures. The right target depends on whether you need to finish combat, answer something, or assemble an engine.
The sacrifice is an additional casting cost. Opponents can counter Natural Order after that creature is already gone, so the exchange carries more risk than an ordinary tutor. A green token can pay the cost, but a colorless creature cannot qualify merely because your deck is green. The creature you find enters without being cast, which also means cast triggers will not happen.
For example, finding Craterhoof with only one other creature often produces much less damage than the same search after creating several tokens. Count the attackers that can actually attack this turn before choosing the finisher; the largest creature is not always the best search.
Build a small target toolbox rather than filling the deck with expensive creatures you rarely want to draw. One strong finisher and a flexible answer often provide more useful choices than several nearly identical threats. Before sacrificing a mana creature, check whether the remaining board actually supports your preferred target and whether you can afford to lose the spell to interaction.
