This is actually for Triptych.

[Entroper]

One word: MULTIPLAYER.  Each player gets the same set of blocks coming at them, but other than that it's completely up to their skill to outscore one another.  Perhaps large combos could rain unwanted single blocks into your opponent's arena, similar to sending lines to your opponent in Tetris.  You can't see what your opponent is doing, only his score and bonus (so very little network traffic, in fact).  Option to play until the first person 'loses' or to continue play until both players stack too high and see who has the higher score.