Mirage Summon is a method of Summon that can Summon a Mirage Monster from your Extra Deck. This method appears alongside Enhance Summon in Qwex67‘s fanfic, Yu-Gi-Oh! Illusion.
Just like how Xyz Monsters are summoned by using any number of monsters with the same Level, a Mirage Monster is Summoned by having any number of monsters with the same Attribute.
(From Qwex67: I like to imagine a Dimensional Wall-like thing made entirely of the Attribute’s real-world appearance appearing in front of the Materials, called the “Mirage Wall”, for example, a FIRE Mirage monster has a Mirage Wall made of fire, then it turns into red-and-orange curtains and draws back to reveal the Mirage Monster )