Mangle was originally designed to be a toy version of Foxy known as Toy Foxy, who would entertain and sing for children sweetly. However children kept thinking she was a toy, and began dissembling and assembling Toy Foxy just before eventually the workers decided to rename her and instead have her go by the name of “The Mangle” or commonly called by her friends, Mangle.

Image and description source: https://fnaf-polebear.fandom.com/wiki/Mangle

(The artist of the image is pole-bear)