STMB Cave (STMBケイブ)
STMB is an air T-Spin technique where you hang an S or a Z over a 3-wide column to create a floating TSD.
One of the easiest ways to spot STMB is to look for 2 columns with equal height, with 3 empty columns in between.
Then you hang a S or a Z:
You can build it anywhere that makes a 3-wide column, and since it is a donation, it will not affect the rows underneath. Here's an example of using it above a C-Spin setup:
Strictly speaking, below is not an STMB Cave. However, it uses the same principle of placing an S or a Z at a 3-wide column.
The above techniques can be used to create Fractals. The third one below is named Fractal Cave. An STMB Cave is built over an incomplete TSD.
It is also possible to use L or J to build STMB.
These are a bit harder to see when you try to build them out-of-order:
STMB can be used on top of an existing TSD to create a shape that gives you two TSDs.
As mentioned above, STMB can also be built with L or J, so naturally, this shape can also be built this way.
Shown below is a relatively common mistake made by players. Notice how the overhang is made on the wrong side:
Compare with this setup:
This shape can be built out-of-order:
A T-Spin shape also has 3 empty columns in between:
So the same principle applies here:
From above, with a little bit of foresight, you can build a shape that gives you 2 TSDs. This specific shape is called Cut Copy, also known as 千鳥格子 (chidori-goshi) in the Japanese community.
Compare Cut Copy with Shachiku Train
Below is not a Cut Copy, but is built similarly:
マジカルキー. Magic Key is a TSD → TST method. The overhang for the TST is built after completing the TSD.
Given its name because of how the shape of the setup looks like a key.
Magic Key is rarely used these days, but it is beneficial in a specific situation like below you don't have the right pieces (in this case, an S or an I; third pic) to create a wall for the TST kick.
Magic Key can be utilized in this situation with the same technique that is used in STMB. The top two lines are skimmed with a TSD, which results in a flat surface, and a wall for the TST kick is no longer needed.
This TSD donation would be another way to create a wall for the TST kick in the above situation, but it would require more minos.
Magic Key can also be made in fields like below. However, Magic Key often results in a large TST overhang, which can be challenging to clean up, so just using an L in this field would be better in many cases.
Once you're comfortable with spotting a 3-wide column and building STMB, these are some things to consider:
Having a 3-wide column doesn't always mean that you have to build an STMB. There might be an alternative way that leads to a more stable stack:
In contrast, below is an example where STMB is a better option compared to stacking. Here we assume that the queue is OIZOTL:
It would be a headache to clean up your rightmost 3 columns to get down to the row marked green if you choose to stack the same way as the first example by having Z as the TSD overhang.
Always be aware of your upcoming pieces. Here is another example assuming that your queue is SOL:
If you don't have a 3-wide empty column, you can make one yourself:
Using the same principle but built out-of-order:
The air T-Spin below uses the same principle as well. Note how two Js make the same shape on the third picture.
In certain situations, you can use STMB to clean up your overhang left after doing a TST.