Mandelbrotverse contains every fractal you can imagine and Cetaverses. Because of this, it also contains itself, similar to The Box.
The largest fractal (the Mandelbrotverse) is a mandelbrot, because at the beginning of the planning process for its creation, the creators wanted the simplest fractals to be the largest and the fastest accessible ones.
Thus, they made the mandelbrot the map onto which every other fractal is mapped, because the mandelbrot set is the simplest fractal that contains complex structures.
Every single other fractal can be found in the center of a convergence point (singularity).
During the planning process, scientists found a simple formula, using which every single fractal could be mapped onto the mandelbrot set, using the fractal's fornula and the mandelbrot set formula.
This was further expanded upon with the Frucz-Klepniw theorem, which states that every single fractal with a finite formula and can be mapped onto a fractal with a finite formula and more than 0 convergence points. It is widely believed that this can be applied to fractals with infinite formulas, but just this problem turned out just like the collatz conjecture (the difference being, that the collatz conjecture was actually solved and proven later on).