Shadow Milk Cookie is a spindly, average height Cookie with powder blue dough and two differently colored eyes: one cyan right eye with a black slit pupil and black eyelashes, and one cerulean left eye with a white slit pupil and white eyelashes. His mouth is sapphire blue and sly, having teeth which change between straight and sharp depending on his emotions. About his right eye is a pale blue, claw-shaped marking. He has white locks of hair near his face—two that fall against his forehead and one slicked back—azure curled sidelocks, and glossy, sharp, long hair in a dual-toned shadow and lapis style that resembles the extents of a jester's hat. Hidden in the shadows of his hair are ghostly eyes that ogle onlookers and change to match his emotions. Shadow Milk Cookie wears an obsidian harlequin bodysuit with turquoise diamond appliques. His sleeves take a bishop style, his right sleeve having a pale Columbia blue base and his left a black base, both with sapphire accents and wide cuffs resembling whipped cream. The jester wears a ruff collar from which hang curling coattails with a ghostly blue lining and a black outside. Upon its lining are more gazing eyes. He wears his eye-like Soul Jam of Deceit as a brooch on his collar in the same place that Pure Vanilla Cookie wears his own Soul Jam. Shadow Milk Cookie also holds a jester hat split into black and cobalt halves, having a milk-splash crown about its rim and blueberry-shaped pompoms at its extending tassels. He holds a thin black staff with a blueberry eyeball handle and another milk design at its neck, its eye-like design being a direct reflection of Pure Vanilla Cookie Pure Vanilla Cookie's own orchid staff.

Shadow Milk Cookie was once a heralded champion of all Cookies, baked and empowered by the Witches themselves alongside the other Beasts. He was granted the divine Virtue of Knowledge, becoming known as the Fount of Knowledge. However, despite his nigh-omniscient perception of the world, he saw how Cookies often shied away from bitter Truths and chose to believe in sweet Deceits instead. Now he is a cruel and manipulative soul, casting himself as a mere entertainer to purposely contrast the destructive consequences of the chaos he sows, to bring about a a world where Deceits and Truths can't be told apart. Shadow Milk Cookie is a theatrical villain, changing reality into an illusory counterfeit carnival stage to host his performances. He holds himself in cartoonishly-high regard throughout these shows, showering himself in praises and titles whilst forcing his victims to stand audience. Unlike what his clownish appearance suggests, he is mercilessly conniving and intelligent, presenting outrageous lies interwoven with bits of truth to entice his enemies to play along. However, such showmanship and promises of clarity primarily serve as a means for him to enforce his own twisted perspectives upon those he seeks to entrap. Shadow Milk Cookie relishes in mocking any and all of his enemies through his shows, especially when such prodding often goads them to do exactly what he wants them to do. Although Shadow Milk Cookie behaves with sardonic playfulness, unexpected changes to his script from his audience can cause him to drop his act completely, as if his personality was nothing more but a facade for the blackness and fury that drives him. Ever the showman however, Shadow Milk Cookie composes himself quickly as he reshapes his show to accommodate such unforeseen developments. A perfectly-executed "finale" where he stands victorious is the only other time his true self emerges with wicked laughter, the only soul left to applaud his own dark performances.