Summa

Just like in Tetris, variously shaped blocks float down from the top, but filled rows do not vanish. Instead, vertically aligned squares, if the sum of the numbers they display is less than ten, may combine into one that displays the sum; if the sum is ten, it will vanish. However, there is another rule that often prevents this merger. Due to my poor command of Spanish I could not figure it out. Unless your Spanish is better than mine, be prepared to experiment.