This is a take on the classic Rock, Paper, Scissors.
Elves beat Giants / Giants beat Wizards / Wizards beat Elves
The important part of this game is the dramatics and the sound effects.
When being a giant you must make yourself as tall as you can. You can use your arms to gain height whilst making a phenomenal roar.
If you are a wizard you must make magic wand waving gestures whilst shouting Harry Potter style spells.
Elves on the other hand make themselves as small as can be, combined with a rather irritating giggle.
Split the group into two teams. Make the teams decide which character they will be and then confront their opponents in two lines opposite each other. On demand from the teacher / instructor they reveal which of the three forms the team has decided to be. This must be accompanied by dramatics worthy of an Oscar
Following the rules above then reveals the winner of that round.