I don't think this game has been done on the forums here before, but I'm not 100% sure.
The way it goes is someone will make a card, and then someone else replies with a card that counters the card the other person made.
...then someone replies with...
Deal 1 damage.
Obviously try to make them a little more interesting than that though
I'll start with this minion:
Flying. Receives 1 less damage from spells.