Xyz Monsters are a type of card in the Yu-Gi-Oh! trading card game. They are unique because they are summoned using two or more monsters of the same level, which are stacked on top of each other as materials. This process is known as Xyz Summoning, and it allows players to create powerful monsters with various effects. Each Xyz Monster has a rank, which is determined by the level of the monsters used for its summoning. They also have Xyz Materials, which are the monsters stacked beneath them. Players can detach these materials to activate special abilities, making Xyz Monsters versatile and strategic options in gameplay.