Ok, after pondering and taking in the suggestions, here is my idea:
Basic idea is the same. The first part of each day is the Vote Phase to determine the Duelists.
The second part of each day is the Duel phase. Here the two Duelists will fight one another. The Watching players may each choose to Assist one of the two Duelists. Some players will also be allowed to perform a Side Action in addition to the assist. The Dark Cabal may also choose one of their members to incapacitate a player as a side action each day.
Now, for the stats:
All Wizards start with the following stats:
10 Attack
10 Defense
10 Health
10 Speed
The Dark Wizards of the Cabal use Forbidden magic to enhance their abilities, and have the following stats:
12 Attack
12 Defense
12 Health
12 Speed
Each player choose an Element at the beginning of the game (Fire, Earth, Water, Air). This is your affinity. All actions used on you by other mages are effected by your affinity. You get X2 effect if they use your affinity and 1/2 effect (rounded down) if they use the opposite affinity and the base effect if they use the other two. (Fire->Water, Air->Earth). Dark Wizards can choose the special Dark element, which does not line up with any of the other affinities. This makes them somewhat more predictable in combat (since they don't have to worry about elemental strength and weakness), but also makes them vulnerable to detection by a Seer.
During the duel each of the Duelists will pick an Element to attack with and will defend with their Affinity. Attacks using the Element Opposite to the defenders affinity will do double damage. Attacks using the same Element as the defender's affinity will do half damage.
Each duel will be done in rounds. At the start of each round an initiative roll will be made to see who makes the first action (so speed can be vital). The winner of the initiative will Attack, and then the other mage will get a counter-attack if they are still standing. The duel ends when either mage has 0 or fewer health remaining.
Observing mages effect the combat by casting an assist spell on one of the mages. The assist is one of the following:
Attack boost (+1 to mage's attack score)
Defense boost (+1 to mage's defense score)
Healing (-1 to all damage the mage receives)
Speed boost (+1 to the mage's initiative)
When making an assist:
Using Fire grants a +1 to Attack actions
Using Earth grants a +1 to Defense actions
Using Water grants a +1 to Healing actions
Using Air grants a +1 to Speed boost actions
The Assist and what Element is used in the assist is shown to everyone.
The Attack action is resolved as Attackers total Attack +/- random(10) vs Defenders total Defense +/- random(10).
Damage is the Total attack number - the Total defense number.
Special Roles:
Duelist Roles: These wizards are skilled in magic that effects the Duel, and may have advantages in the Duel themselves
War Mage: Has superior offensive magic, and can grant a bigger then usual offensive boost to another mage when assisting a Duel.
+2 to Attack attribute
+1 to all Attack Boosts
Battle Mage: Is skilled in personal combat, giving them an edge when defending and can grant a bigger then usual defensive boost to another mage when assisting a Duel.
+2 to Defense attribute
+1 to all Defense Boosts
Warrior Mage: Trained in both martial and magical combat, the Warrior Mage can shrug off hits that would incapacitate other mages.
+5 to Health attribute
Time Mage: Skilled in manipulating the energies of time, the Time Mage is swifter then most other mages, and can grant a bigger speed boost to other mages.
+2 to Speed attribute
+1 to all Speed Boosts
Healer: Has powerful Healing Magic
+2 to all Healing actions
Subtle Wizard: He specializes in casting magic unseen, and his Assist actions are not reported to the other players.
Archmage: A very powerful mage, he has a major advantage when dueling other mages.
+5 to all attributes
Side-Action Roles: These wizards can take actions during the Duel that effect other mages not in the Duel.
Nullifier: Skilled in the ways of anti-magic, the nullifier can choose one mage each day and prevent them from effecting the Duel.
Enchanter: Using their enhanced mind magic, the Enchanter can prevent another Wizard from taking any side-actions that day.
Guardian: Carefully watches over another Wizard and can prevent them from becoming incapacitated by side-actions during the Duel.
Oracle: Can use their magic to see if another Wizard performs any side-actions during the Duel.
Justicar: A Wizard seeking the destruction of the Dark Cabal. Can examine a Wizard as a side-action to determine if they are part of the Cabal.
Grey Mage: Taking justice into his own hands, he can incapacitate a player each day as a side-action.
Seer: He can examine one player each day as a side action to learn their Affinity.
I'm going to try making up a program to run the duels. Once that's made I'll run through a bunch of tests and adjust the numbers as necessary.