A TSD → TSD setup. Called "double dagger" in the Japanese community.
Fractals can also have a gap between the two T-Spin shapes:
Fractals are usually built when you don't anticipate getting a T soon. There are four main ways to build a Fractal.
Fractals are most often and most easily built on top of an existing TSD.
This pattern of repeating LSJZ is a useful stacking pattern in general and is the basis for LST Stacking, which is essentially building Fractals on top of Fractals.
The above pattern can be built with alternate pieces:
See LST Stacking where these alternate pieces are more extensively covered. Example:
Using STMB Cave and Co. is another a popular way to build a Fractal.
STMB Cave can be used over an imcomplete TSD to create something called a Fractal Cave:
LT Stacking is a stacking method where you repeat L on the left side while using the T to do a T-Spin Double. No one uses this stacking method anymore in Ultra, but it is still a useful technique to use to create Fractals.
The cleanup after doing the two TSDs is tricky so it's relatively rarely used. Example:
As a sidenote, the L will leave a block on the column it was placed, which is useful in several situations:
This is perhaps the least commonly used technique to build a Fractal because it requires more planning of your pieces. Reminiscent of building DT Cannons. Examples:
This method works well in conjunction with Fractal Cave as a follow-up to build a Fractal.
Just like DT Cannon, alternate pieces can be used to make the same shape that the L makes.
A common mistake that people make while building Fractals is building the overhang on the wrong side:
For this example, the resulting field is clean enough to recover with a DT Cannon, however.
Compare Fractal with DT Cannon:
Fractal would be the better option in the majority of cases if there's an extra row underneath.
This stacking pattern which utilizes STMB Cave can be used to create shapes similar to Fractal.
Note that repeating IJ makes the same shape:
See the Imperial Cross page to read about some differences between Fractal and Imperial Cross, another similar TSD → TSD setup.