"They read everything you are afraid of-
I.E. they read what you do not know."Fears are very quick, agile creatures who use what you're afraid of against you. They use their sharp beak-like heads to pierce their opponent and have the ability to root them into the ground. Once they have stabbed through someone, they can read what it is their afraid of and use it against them.
Fears were first encountered in the comic in the second chapter, having breached beyond their usual territory to the Pool of Tears, where they attacked RGB and Hero, giving the latter her Schism. They later appeared in Chapter 6 when Hero and RGB argue and separate, alongside a number of Doubts and a very large Grief, cornering RGB up until he turns Negative, where he kills them instead.
Fears, despite their unpleasantness and danger, appear to be a useful commodity to those in The World of Make Believe. Hobby, notably, is a fear-monger in The Black Market, which is to say, he sells the remains of these creatures. It is unknown what they do for people, but even dead they are still dangerous to handle.
Negative RGB has also put Fears to good use, weaponizing them against the other creatures in The Plains of Hesitation by attaching one of their sharp heads to the end of his cane. This makeshift scythe is an extremely frequent piece of imagery that appears alongside Negative, in both fan and official art alike, making it his most recognizable trademark.