My idea may seem complicated, but...
Elements of RoundTwelve teams (one or two players by team), one per element. Each round, the teams are shown in a circle, like this :
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First rule :All teams start with 20 points. During a round, a team (called A) can
challenge one opponent (called B). B may not be challenged by any other team this round. B can refuse the battle if he has posted after A, but loses 3 points.
In other words, if you post early, you can choose whoever you want but you won't be able to refuse a battle.
Second rule :You must have the Mark of your Element, but you can use any cards from your element or the 2 adjacent elements on the circle (+ Other cards)
For example, with the circle above, Death Team may use Mono Darkness with Death Mark...
Third rule :If you are victorious, you earn 2 points. The adjacent elements' teams earn 1 point.
If you are defeated, you lose 7 points.
If a team which has no more points can not play (and earn points) anymore, but stay in the circle.
Last rule :At the end of the round, teams which have fought
swap their positions in the circle (in the order of the challenges).
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About the length of the event : total amount of points is 240, and every challenge (accepted or not) decrease it by 3 points. So, there would be maximum 80 matches...
That's it.