Voldermort was the Shadow because he was extremely powerful and dangerous.

Albus Dumbledore was the Mentor because he guided and protected the hero by offering advice weapons and other gifts.

Professor Quirinus was the Threshold Guardian because he stood in the way of the hero at important turning points.

Professor McGonagall was the Shapeshifter because he can transform their shape and appearance.

Hermione,Hagrid,and Ron was the Ally beucause they helped the hero in moments of crisis.

Hagrid was the Herold because he acted and a sign of comeing change.