I believe what he means is that for each pair they will have their own individual round together with a sequence of duels, each duel taking place in a particular mod until the win condition for that duel is met. This stipulation means that you can not have two duels take place using the same mod, with that opponent. So for instance if you did Lenshu for your first duel, then neither of you would be able to select that one again for that round, the mod must change each duel set. At least this is what it sounds like to me.