I haven't played it yet, but I have some ideas.

Dragon Knight

Once a brave and loyal knight to Westlock, he went out to slay down the Dragon Goddess. But he got seduced and claimed by her. Now he fights for her reason. Equipped with dragon scale armor and the holy flame sword he can mount dragons he casts. He accepted to fight in the Arena to win more followers for the Dragon Goddess. Then, she can start her burning crusade to burn all non-believers. There are rumors that he is associated to Arraxian Crown.

The Dragon Knight is hybrid of War and Fire school. He has some special equipment spells that only he can cast and wield the flame sword.
He can cast a dragon he can mount and perform an special attack, that requires the dragon and the knight to be ready. They also can do normal individual attacks. While riding a dragon, he can only cast Incantations, Enchantments and Attack spells.
His second special ability can return fire attack spells from the discard pile for the cost of life points.
The Holy school cost triple while spellbook creation.

Another idea is a demon hunter, a hybrid of Arcane and War school.

Affiliated to Sortilege a powerful one man army, but he is low on casting creatures. Any creature spell cost him triple. His "only"-equipment can be powered with mana like the Voltaric Shield.
I thought about an special ability against the Dark school, but maybe to special and situational.