Geist-Fueled Scarecrow’s ability applies to creature spells even if you’re casting them for an alternative cost (such as that of emerge). If you cast a creature spell without paying its mana cost, you’ll still have to pay .

Abilities that reduce the cost of a spell apply after abilities that raise them. For example, Bedlam Reveler will cost to cast if you have seven instant and sorcery cards in your graveyard while you control Geist-Fueled Scarecrow.