Back-to-Back T-Spin Triple
From Hard Drop Tetris Wiki
Back to Back T-Spin Triple is a difficult maneuver, which sends a total of thirteen garbage rows to the opponent. It requires the player to make two T-Spin triples back to back.
LT/JT, the simplest set up-- flawed due to its heavy dependence on T pieces.
LSI/JZI set ups.
LJS/LJZ set ups, versatile due to their interchangeable core.
A player may switch sides to clear Back to Back T-Spin Triples indefinitely.
Any T-Spin is good enough to keep the "Back to Back" alive, which allows for lopsided designs.
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Note that the previous 2 designs have interchangeable second parts.