Brainchild

A rumor can become so vivid and persistent that it comes to life, creating a brainchild—a living illusion that hatches from an intense belief in a remorseless and implacable killer. Often, these rumors are borne from victims of a @UUID[Compendium.pf2e.spells-srd.Item.Vision of Death] spell. A brainchild's capabilities grow when they pursue a believer but deflate against skeptics, making them only as dangerous as one believes them to be. A simple drive to stalk, terrify, and kill propels a brainchild, but the creature might also exhibit other behaviors ascribed to them through gossip.