The Fractal is a device which can enhance a person's traits by collecting fragments of their infinite multi-dimentional selves and infusing them into said person. The results vary wildly, sometimes changing mentally, physically, or both, and in unpredictable amounts. ( for example: When Doc emerged his only physical difference was his eye color yet he gained considerable mental clarity. When Annalise emerged her entire body had transformed into that of a tiefling yet her mental state remained relatively the same.)
The way the Fractal functions is still not entirely understood. One thing that is known for sure is that entering it more than once is disastrous and nearly always fatal.