This is a question I've had since I first played this game, maybe twenty years ago. I would say that it is random, given the nature of the game. However in my experience; the O-blocks never come alone (after you get one, the chance of getting another seems more likely). I also feel that you get the I tetromino just after you made a mistake.
I've been googling this for quite some time and haven't found a conclusive answer. Can somebody please help me? I've only played the game on the original Gameboy.
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block is much less frequent than the others, which makes it impossible to play perfectly. Very annoying.----
blocks, followed by another piece, then two more----
blocks... It was at the highest speed setting. I think I eventually got bored and quit. Must've been a weird fluke in the programming.