Originally, it's existence was only known through its familiar and was not made public until Chapter 10 when it was revealed to be the witch form of Ui Tamaki.
The Happy Witch. Her nature is suffering. A “half-witch” who quietly grows within a membrane-enclosed womb, absorbing nutrients from the impurities released when Puella Magi become witches, the emotions that humans emit, and so on. In order to stabilize the contorted power she holds, gemstones are scattered across her body as she grows. When she eventually breaks free of her shell and matures, the newly-unchained witch will hungrily absorb all the energy there is. Should she swallow the entire planet, her feeding will likely continue unabated until she becomes a giant mass of cosmic matter.
The witch of happiness. Her nature is suffering. A “half-witch” whose energy has stabilized after being enclosed in a contracted membrane. Having lost a precious part of herself, she now shakes the earth indiscriminately in order to fill the empty hole in her chest. Her rampage likely will continue unabated until a single girl is sacrificed. Also, should she lose the membrane surrounding her, this half-witch will be unable to maintain her physical body, and will eventually melt into the atmosphere. Nobody can know what effect the impurity scattering away from her may bring.
Minions of the witch of ???. These swallow-like Familiars are everywhere in Kamihama. They seem to be collecting magic as offerings to their Witch. They target Magical Girls and steal not only their magic but also their memories, visions, and even emotions. They have also been known to target other Witches. Hunting in a group, they utilize their anchor-shaped legs to capture them. They are uninterested in normal humans without magic, because they don't make good offerings.
Minions of the Happy Witch. Their role is to present offerings. The witch’s swallow-like minions, who are collecting magic energy as offerings for their master. Several of them can gather together and whip up strong tornadoes, with which they collect nearby objects into a nest. They then store magic energy in the nests, where they make preparations to offer it to the witch. Their goal is to save their master in every way possible. Upon losing their master, they would ordinarily become unable to fulfill their role and vanish, but it seems that they’re still hard at work in a different form somewhere else.
In Magia Record
|Warning, this section contains spoilers.|
A massive “half-witch” body surrounding Ui Tamaki, which the Magius are incubating below Hotel Fenthope for the majority of the game’s first arc. Ui’s powers are the source of the Doppel phenomenon, absorbing impurity from the Soul Gems of Puella Magi within the city. The Magius planned to use the energy from the transformation of Eve’s Grief Seed– and the destruction of Kamihama City– to expand her range of influence to the entire world, which would both shut out the Incubators and continually provide the rest of the universe with energy from Doppels.
Ui, Touka and Nemu’s wish was to steal Kyuubey’s energy-collection abilities, in hopes of creating a system to prevent Puella Magi from becoming witches. Unfortunately, the initial rush of collected impurity threatened to turn Ui into a witch on the spot. As damage control, Nemu summoned an unseen Rumor to remove Ui’s identity as a human being, and stored it in the newly-disempowered “Little Kyubey” for safekeeping. Without any mind or emotions, Ui’s body was at no immediate risk of turning into a witch… but as a side effect, the other Magius’ memories of her were removed as well. With no memory of Ui, their time together, or their original motivations, the Magius’ plan went in a much more dangerous and self-serving direction than it otherwise would have.
After the Little Kyubey reunites with Ui’s body and the Magius regain their memories, they help Iroha rescue her from inside Eve. Once Ui reawakens, her powers seem to be under control, and the crisis seems to be over for now.
- Originally the Oscars had no name in their description card, only "????". This changed after the release of Chapter 10 in which the witch they serve and their descriptions were given more clarity. They have, in fact, two separate description cards present in the game's list of witches, rumors and familiars.
- "Shitori Egumo," which means "I'm going alone," is taken from a poem by Kenji Miyazawa. He also wrote Night on the Galactic Railroad, which Iroha, Mifuyu's and Yachiyo's doppels take their names from. He also [wrote] [the] [works] where Kuro's, Nemu's and Touka's doppels take their names from.
These posters were put up throughout Japan in order to promote a new event. The pictures are taken from this website.