YGO Structure Deck: Shaddoll Showdown - Rules of Play says:
Originally introduced in Duelist Alliance, Shaddolls combine Flip Effects and Fusion Monsters to surprise your opponent. Powered by the incredible Shaddoll Fusion Spell Card that lets you Fusion Summon using monsters in your Deck, Shaddolls can Summon “Shaddoll” Fusion Monsters of any Attribute and stack up powerful Graveyard effects at the same time! Shaddoll Showdown offers new monsters that break the rules of what a Shaddoll monster can be, a full selection of the cards you need to build a Shaddoll Deck, and more.