I thought it was time to pitch something a little bigger to what I'm used to...
The basic idea is an arena where gifted magicians and sorcerors of both sexes are confined to a small space that they cannot leave. There is a distance between them, and to leave the small circle that they stand in is to lose the battle. There for, they must rely on magic and cleverness to force the opponent to bail their circle.
Summoning monsters and control of elements, plus manipulation of the fighting arena is all standard, and more ideas could come up as players show interest :)
A standard battle could involve the fighter raising the ground around his/her opponent, lifting them up to a pillar, but never actually manipulating the circle they are in. Then they could summon demonic birds of prey or other flying creatures to attack the pillar and make it fall. How they could counter this could be a number of ways. Levitating the patch of ground back down, for one, but that would leave them deep in concentration and at a disadvantage, easily blown off the circle with a fireball or gust of wind.
I'd encourage some clever strategies, and I'd really like to see some attacks/counter attacks/defenses that really bring an omg, genius! Kind of reaction.
As for the mood, it could go anywhere from complete morbid seriousness to cutesy over the top anime. The latter is something I'd definitely like to try.