MacGuffin (a.k.a. McGuffin or maguffin) is a term for a motivating element in a story that is used to drive the plot. It serves no further purpose. It won't pop up again later, it won't explain the ending, it won't do anything except possibly distract you while you try to figure out its significance. In some cases, it won't even be shown. It is usually a mysterious package/artifact/superweapon that everyone in the story is chasing. Your task is to design an object under the trope of a MacGuffin that seems completely ordinary, however is desired by all parties in your desired plot.