Triple Double (TD)
Triple doubles are the best way to activate triples in a game
A TST → TSD setup. A powerful setup to use mid-game. Assuming that you have been maintaining back-to-back, you will send 12 lines, just like DT Cannon.
TDs are mostly built the same way as TSTs are built. The only difference is that you have an empty column underneath at a specific position.
TDs are most easily recognized and built when you have a notch above an empty column.
Using the JL combination is not the only way to create a TD when you see a notch:
Whenever you see this two-step stair, you can consider building a TST.
The two-step stair can be created yourself by covering a TSD shape with S or Z. The rest is built the same way as you would build a TD from a two-step stair.
Compare with this TSD donation.
When it's a one-step stair, you can use S or Z:
Here's an example using this pattern with some forecasting:
When you use JL to build a TD, it is given a special name of C-Spin. Given its name because of the characteristic C shape that JL forms. You can build TDs this way whenever you recognize a notch that has the same shape as marked as green below.
Note: The Japanese community refers to C-Spin when they say TKI, whereas the western community often refers to this opener when they say TKI.
TDs can also be built after this specific TSS donation that leaves a notch. These are usually done because you can't fill in the required block to do a TSD donation.
The above TSS donation would become a TSD donation if you fill in the right block.
Here are some examples:
TKI積み. C-Spin can be used as an TST → TSD or TST opener. The blocks marked skyblue on the second picture below are filled in free-style. Players often build another TST after the first TST.
There are a couple of perfect clear patterns that you can build with your second bag. The chance itself isn't high, but it's something that's nice to be aware of.
TDs are useful when you have a bad overhang such as below. Note that you can achieve the same effect with an Imperial Cross (third image). However TDs are often preferred if you have a choice to build either.
Below is not an uncommon situation where you would use I and S to build a TD.
- テトリステンプレ集＠テト譜 on C-Spin
Skimming to create shapes is not recommended as it is almost always possible to avoid skimming if you stack correctly. Nevertheless, it is a useful exercise in understanding how the shapes are made. Below are some examples of building TD with skimming: