I've been creating new games as soon as matches finish and the new match-ups are determined.
If you refresh your browser you can see the current bracket. I've sent out 3 of 4 Round 3 matches. The last Round 2 match is nearly over.
So there are basically 8 people left.
Unfortunately only the first part of these companion tourneys will usually count for the challenges. It just takes too long for games to finish. I've thought of trying a semi-speed tourney where you get points for taking your turns in under 12 hours...
