Okey-Cannon

The Okey-Cannon is a specific DT Cannon invented by the Tetris Player Okey_Dokey. This Opener can be used in games that follow the Tetris Guideline. It results in a T-Spin Double followed by a T-Spin Triple in the first 3 bags whereas the field is pretty flat after 2 bags.

The Build
The first bag is stacked in the following 2 ways which only differ in the I piece placement (in the second bag the I piece will be placed in the other location). The first way will always work when starting with an L piece and a T piece whereas the second way will always work when starting with L, J and O. Both ways result in a weird overhang originating from the S placement. This overhang will be fixed later with the help of a Z piece.

The second bag will always lead to the same stack. The Z piece must always be softdropped. The T piece is kept on hold until the very end, so a T-Spin Double can be made.

In the second bag the Z placement is hard to execute if the S piece is placed beforehand (which cannot be prevented every third time). In this case, the Z piece must be rotated counterclockwise 5 times while holding down the softdrop button whereas no sidewise movement is allowed simultaneously. Once those 5 rotations are done, the Z piece still needs to be moved right to reach the desired location.

The Third Bag
The Okey-Cannon can lead into a Perfect Clear after 8 cleared lines in total. The PC rate (amount of PCable third bags) lies at 56.4 % which is the highest any DT Cannon opener can achieve. If the T piece comes early in the third bag, then it's best to perform the T-Spin Triple immediately. Afterwards continue with Downstack or try the mentioned Perfect Clear.

In fact, the Perfect Clear can always work, if the T piece is placed first and no garbage lines have been inserted yet. Here are all Perfect Clear solutions. Note that the I piece is always placed in the same location and either Z, S or O are missing (kept on hold).

Here are some S, Z, O, L and J placements that will guarantee the PC for the remainder of the third bag (provided the T-Spin Triple was made beforehand). All placements in the 3 left-most columns will not block the needed lane for the T-Spin Triple, thus they can also be made before the T placement. Sadly, such a placement is not possible for the Z piece.

If the T piece comes late in the third bag, then it can be better to postpone the T-Spin Triple and make a T-Spin Double instead. In this case, you will create a floating T-Slot with the overhang on the right side and either S & Z or L & Z on the left side.

A C-Spin (Triple Double Attack) is also a possible follow-up.

Different Order of Z Placements
In the first 2 bags it's also possible to place the Z pieces in the reversed order. This has the advantage that the second Z piece mustn't be softdropped (which must be followed by 5 spins sometimes).

However, there's also a 33.3 % chance that the specific DT Cannon can't be built. This happens, if the Z piece arrives after S & T in the second bag. In this case, it might be better to give up on a DT Cannon entirely and create a T-Slot instead. This can be done by softdropping the S piece under the overhang.

Other Placements - same Result
This section lists some further ways to build that specific DT Cannon in the first 2 bags. All ways have in common that there's a 33.3 % chance in the second bag that the build will fail. Note that the T piece is always placed vertically, and in the first bag L and J will be placed on different sides (those are direct consequences from column parity).

This way will work when starting with L, J & O. It will fail in the second bag, if the Z piece comes after J & T. In this case, it's usually still possible to continue the build by making a T-Spin Single and burning a Single (instead of the T-Spin Double).

This way will work when starting with I, J & T. It will fail in the second bag, if the O piece comes after J & T. In this case, it's usually still possible to continue the build by making a T-Spin Single and burning a Single (instead of the T-Spin Double).

This way will work when starting with I, L & T or I, J & T or I, L & O. It will fail in the second bag, if the O piece comes after Z & T. In this case, there are numerous possible cop-outs. Note that the first picture represents the same build as above but with different order for the O placements.

This way will work when starting with L & J or L & T. It will fail in the second bag, if the O piece comes after Z & T. In this case, there are numerous possible cop-outs. Note that in the first bag the I piece can also be placed on the left side.

This way will work when starting with L, J & T. It will fail in the second bag, if the Z piece comes after S & T. In this case, a T-Spin Double cop-out is possible similar to how described under Different Order of Z Placements.

This way will work when starting with L & J or L & T. It will fail in the second bag, if the O piece comes after Z & T. However, there's still a chance that an alternative solution will work that involves a horizontal I placement. When considering this alternative, the build chances increase to 72.8 % in the second bag. Note that in the first bag the I piece can also be placed in the third column but then the alternative solution isn't possible anymore.

The last shown way is probably the best alternative to the standard Okey-Cannon because it has the lowest demands in the first bag and the highest build chances in the second bag. An early second Z piece may prevent the DT Cannon build but then it's still easy to set up a T-Spin Double as cop-out.