Fractal

Fractals (sometimes also called Spider) are also known as TSD stacking. This is one of the most common T-Spin methods used in multiplayer. Be wary that it can be difficult to build these without using T-blocks in the stack, therefore presenting significant risk in the event that you do not get enough T-blocks in time for the execution. This pattern can be used to make a stack indefinitely high, but setups stacked three or higher are rare.

Japanese people use the term "Double Dagger" (Double Decker) instead of Fractal.

Fractal 1
Two or more T-Spin Doubles layered above one another in the following even shape.

Fractal 2
Fractal 2 is a similar idea to Fractal 1, however the shape is uneven. Notice that with F2, the hang must be on the correct side to avoid blocking the hole.

Fractal Cave
An STMB Cave over an incomplete T-Spin Double. This situation is not uncommon after the T-Spin Triple in Triple Double.

Two T-Spin Doubles
By changing the position of the overhang, you can change from fractal to an Imperial Cross.