From Hard Drop - Tetris Wiki

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.

without L piece

Okey's Plank with L piece

is best opener after 2 rotations

and softdrop after 4 rotations

and softdrop after another rotation

and step to right

The Third Bag

There are several options how the Okey-Cannon can be continued in the third bag.

Perfect Clear

It 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 among all DT Cannon openers. In fact, there's always a PC solution, if the T piece is placed first in the third bag (T-Spin Triple). Note that the I piece is always placed in the same location and either Z, S or O must be kept on hold for the PC to work.

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 placement is never possible for the Z piece.

Center 4-Wide

Okey-Cannon can lead into a center 4-wide Combo Setup. If possible, use the T-Spin Triple to counter incoming garbage.

Center 3-Wide

In a similar manner, a center 3-wide combo is also possible. While center 3-wide is not as powerful, it offers a higher build chance, if both L and J come early in the third bag.

Downstack Combo

The third bag can also be used to prepare a downstack combo. If garbage is inserted before the third bag, then the knowledge of the garbage column can be used to make a better decision. If the empty column shows up on the right side, then build a tower on the left side. If the empty column shows up on the very left, then build a larger hill on the right side and even out the left side.

I-Spin Quadruple

In the very unprobable case that 4 rows of garbage show up with the holes exactly below the T-Spin Triple, an I-Spin can be used to get rid of that garbage. The order of the Quadruple and the T-Spin Triple doesn't matter. Rotate the I piece twice before moving it under the overhang and then rotate it counterclockwise. This will also work if an S piece was placed vertically on the left wall beforehand. In this case, rotate the I piece clockwise twice and then counterclockwise.

Note that the behaviour will be different in the mirrored build. Here you don't have to rotate the I piece before moving it under the overhang. However, an I-Spin will not be possible, if a Z piece was placed vertically on the right wall beforehand.

Postpone TST

If the T piece comes late in the third bag, then it can be better to postpone the T-Spin Triple by one bag 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.

C-Spin

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 in the first bag the T piece is always placed vertically on the right side, and L & J will be placed on opposite sides.

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.

Best Alternative Version

The best alternative to the standard Okey-Cannon is probably the one with the I piece placed horizontally in one corner and the T piece placed vertically in the other corner. Here are some reasons for it:

If the O piece comes late in the first bag, the player can have a look at the first pieces of the second bag to decide where to put it: The left side is favorable if the second J piece shows up early and the right side is favorable if the second Z piece shows up early. This improves the chances to complete the build beyond the default 66.7 % - it's 75 % if the whole second bag can be seen beforehand (no build will work if the second O piece comes after J, Z and T).

If the first O piece is placed on the right side and the J piece shows up too early, then a DT Cannon can still be stacked in the following way (the third I piece is needed to complete the build):

If the first O piece is placed on the left side and the Z piece shows up too early, then there might still be a chance to stack a DT Cannon in the following way (larger Z piece overhang):

If the first O piece is placed on the left side, then there is also a good chance to stack a Cut Copy in one of the following ways:

See Also