Milly is a fan made antagonist on Abandoned: Discovery Island.
She appears to be a classic, Grayscale version of Clarabelle Cow.
She starts at night 3 in The Broadcasting room. When in the office, the player must shut off a camera or she will kill you.
Milly starts in The Broadcasting Room, then she goes to Character Prep 1, Staff Area, Meat Freezer, and then the office.
Her name originates from the "M" standing for Moo, which is the noise that cows make. And " illy" Which is what some other classic toons like Willy are called.