A Fusion Substitute Monster (融（ゆう）合（ごう）素（そ）材（ざい）代（だい）用（よう）モンスター Yūgō Sozai Daiyō Monsutā) is a monster with an effect that allows it to replace a single specifically named Fusion Material for the Fusion Summon of a Fusion Monster (with the exception of "Shaddoll Core", which substitues for Attributes instead), as long as the other monster(s) used are the correct one(s).