Duels against zombie players.
I often find myself playing against people who don't make a guess at all. Or the fist guess is random and then nothing else. Please make that an instant knockout, so we don't have to go through 2 or 3 rounds waiting for nothing. (you snooze, you lose!) And don't give that player experience points; seems like a loophole for levelling up. For the rest, I love the game mode.