For the first time I'm submitting a non-smw TAS. One because I'm holding off on submitting anything until after Six Pack is done and two, I just don't feel like only doing smw. Anyway, here is my Tetris DS TAS that aims to beat Marathon mode as fast as possible.
I didn't go for many Perfect Clears or anything because that'd take too much time to think of. instead, I use the standard method for professional sprint tetris that is 6-3 stacking. What this is is stacking up 6 wide on the left, and 3 on the right (And vice versa) using 3x4 boxes. What this does is it reduces the amount of key presses it typically takes to get each piece where you want, and makes the tetrises not take any more than 2 key presses (Disregarding hard drop). Learn more about it here.
After about 130 lines the pieces fall too fast to do 6-3, which is where we transition into the classic 9-0 stacking, where the well is all the way on one side, as many tetris players, old and new, may recognise. There's not really much to say after this point. It can probably be improved with better piece placements since I'm only probably intermediate at modern tetris (And I couldn't do the typical 6-3 start since there was no early T)