From Hard Drop - Tetris Wiki
The Double Triple Cannon 2, also known as the DT Cannon 2, Double Triple 2 or DT2, is a variation on the Double Triple Cannon. Rather than having a "large notch" (as with the DT Cannon) that is cleared by a T-Spin Double followed by a T-Spin Triple, in the DT Cannon 2, the T-Spin Double and T-Spin Triple are cleared by separate notches. However, similarly to the DT Cannon, the DT Cannon 2 does have a notch for the T-Spin Double on the same side as its overhang.
 Wall-Overhang Variation
This is the preferred way to set up the DT-Cannon 2.
 Empty Field Setups
 Situational Setups
 Wall-Notches Variation
The wall-notches variation of the DT-Cannon 2 is actually one of the harder setups to master. It can only be made by transferring or trimming blocks, therefore it is only practical in mid-game.
 DT Cannon 2 STSD
This setup looks identical to DT Cannon 2, with the only difference that one further cell is empty at the bottom (marked light grey in the first picture below). It results in a STSD after the first T-Spin Double is cleared. So, it's usually 3 T-Spin Doubles in total.
 See also