Fiddlesworth

This stacking method, discovered by fiddlesworth, produces 12 garbage lines in Tetris DS standard vs. mode. It requires Hold piece and SRS.

You can perform this stack from an empty playfield if any of the following is true of the first bag of seven tetrominoes: It is especially useful if your first tetromino is S or Z, but it does have a speed penalty on games with a slow soft drop.
 * S before J
 * Z before L
 * J before S before T (hold the J)
 * L before Z before T (hold the J)

Start with an S–J or Z-L:

Build it (S and J depicted)

Soft-drop a T and spin it:

Build it more. You'll need to soft-drop the S, and you'll need to switch the O and Z if you got Z before O in the first bag:

Soft-drop a T and spin it twice:

And it leaves room for a back-to-back T-spin single (3 garbage).