Hodge-podge
In this usage, a work is called a pastiche if it is cobbled together in imitation of several original works. As the Oxford English Dictionary puts it, a pastiche in this sense is "a medley of various ingredients; a hotchpotch, farrago, jumble." This meaning accords with etymology: pastiche is a French word, coming from the Italian term pasticcio, refering to a kind of pie made of many different ingredients.
Some works of art are pastiches in both senses of the term; for example, the David Lodge novel and the Star Wars series appreciatively imitate work from multiple sources.
Read more about this topic: Pastiche