Overview
Details are unknown as of now. Currently the witch is announced to be the witch form of Mami Tomoe, appeared exclusively for the game version for the anime.
Appearance
According to the most recently posted screenshots, her costume looks about the same as her Puella Magi form except longer with a cat icon, wearing yellow stripped stockings and a yellow skirt turned upside down shaped hat. Her hands also seemed to have changed into two extremely long tentacles. Appeared to be humanoid form more than anything.