Game idea, maybe stupid: Tic-tac-toe, large grid but with some random noise (a boulder landscape tossed onto the board) blocking some cells. Win by getting 4 in a row. The loser gets one final "revenge move" and lose if they can't also get 4, but win if they can. This means the first/leading player actually has to make blocking moves which perhaps shifts the dynamic back and forth and also disrupts the landscape. Played a game against myself. Went on for a while, but might be predictable.