My copy of The Opal Deception has this cover:

I can see that the male in the suit and tie is Artemis, and the person next to him is presumably Holly, and the person on the screen is naturally Opal. But what is the red, furry creature with horns on the cover? It doesn't appear to be humanoid, like humans, fairies, or trolls, but I don't know what it might be. What is the red furry creature?