Witch Design by Gekidan InuCurry.
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 ribbons. Appears to be more humanoid compared to other witches.
Apparently, the very first Candeloro submitted illustration in pixiv is apparently a personification of the witch itself. Which goes without saying, illustrations related to the personification of the mascot itself has a higher ratio than the real thing.
Candeloro in pixiv
As soon as the announcement is released, the submission ratio for both Mami Tomoe and Witches has since increased, apparently as the result of simultaneous submissions from both sides of fans.
Since both Canderolo and Charlotte share the same boundary motif, it won't be surprising to see both of them getting paired together in future illustrations.