Goblet of Fire (object)

The Goblet of Fire is a magical object that is used for the Tri-Wizard Tournament.

Usage
The Goblet acts as an unbiased judge, knowing about each candidate who puts their name into the fire, including their school and their age. By knowing the school, it is able to pick a name at random from those specific students, so it does not accidentally choose two students from the same school. And by knowing the age of the student placing their name in, it can reject underage students and as punishment, temporarily age the students into an elderly age.

It also creates the tasks which the selected challengers have to combat. These tasks are controlled by those running the game, scheduling the tasks so the circumstances of said tasks are more controlled. However the Goblet has a magic that will, in some way, make the challenger inevitably face their task, regardless if they do so willingly or not. For example, for the task of retrieving a golden egg from the dragon: if a challenger tried to opt out of the task, the Goblet's magic will cause an unforeseen circumstance where the challenger will have to retrieve a golden dragon egg from a dragon. Once the name is picked from the Goblet, the person is bond to the Tournament until the end, and cannot forfeit.

As powerful as the Goblet is, it can be manipulated by power dark magic, to confuse it and get passed its defenses to make a position for a fourth candidate.

Trivia

 * Everything about the Goblet creating the tasks and having some fate-binding magic to the challengers is completely absent in the official canon. Chase made that as a reason why Harry could not forfeit, and felt that instant death from forfeiting would go against Dumbledore's character in hosting the Tri-Wizard Tournament.
 * While this ability information is stated in notes and comments, of the fic, it isn't stated or shown in the fanfic, as neither Harry nor any of the other challengers tried to forfeit.