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I'm all for duels. I wouldn't say that few people are interested. I think people will gather (there are still people in the counter-hero theme in duel mode), because playing a few standard duels takes significantly less time than playing maps or RTA (Real-Time Attack).
Regarding the conditions, here's a possible option:
1. Game 1: Allow the opponent to choose 6 heroes (or another number, at the organizers' discretion). Player 1 chooses the first hero, then Player 2. (They cannot be changed).
2. Game 2: Players switch heroes.
3. Game 3: Allow the opponent to choose 6 heroes. Player 2 chooses the first hero, then Player 1.
4. Game 4: Players switch heroes.
The conditions are, of course, not new. But in my opinion, they are quite interesting.