Juno is a devious sorceress and potential foil for MarzGurl. Potential in so much as she seems to be quite inept, and her aspirations (modest though they may be) are beyond her abilities. Her first appearance was in "Marzgurl Discusses Final Fantasy XIV" where the discussion of fantasy seemed to draw her attention.
Marzgurl herself does not seem concerned with Juno beyond occasionally being annoyed, and in fact rather views the mystical madam as a sort of "doofy friend," who simply doesn't know any better. So far her only plot of note has been to try to torture Marz by making her watch the sequels to The Land Before Time. While it's certainly not a pleasant experience, Juno seems to have come out of the deal far worse, being reduced to a huddled, gibbering lump.
Juno wears a black hooded cloak and carries a long, gnarled wooden staff with a magical orb on top, which she uses to cast her magic. Otherwise, she is remarkably similar looking to Marzgurl, though whether this is magical illusion or some more convoluted, Insano-esque explanation is as yet undetermined.