Firebrowl made a post talking about minigames for warriors (Jousting). This post is my idea of a mini-game for Mages instead.
Clashing. Like in Harry Potter where Voldemort and Harry shoot Magic at each other, and the beams struggle back and forth like tug of war. Mages could do something similar.
To win you’d have to press certain buttons in a certain order, if you press incorrectly you start losing. If you successfully finish 5 buttons in a row, you start winning. Until eventually someone falls too far behind and dies. Kind of like Arcane Adventures.