The Shadow was the most dangerous creature from the Inkworld that was made up of many mystical creatures, such as trolls, fairies, and other creatures.
History
Fenoglio created The Shadow as Capricorn's pet hound in Inkheart. It was said that Capricorn used trolls to make it, and then killed those trolls. It was made of up of fire and ashes and had two sharp eyes but no face. Meggie Folchart was forced to read it out by Capricorn. Due to Fenoglio's modifying of the written words of the book, the Shadow was forced to remember all the lives of those it had killed and betrayed Capricorn by destroying him instead, soon followed by destroying himself.[1]
A sort of different version of the Shadow came along, summoned by Orpheus. It originally was summoned to follow Orpheus's commands, scare soldiers and ruin Mo and Dustfinger. It was, again, killed after holding Brianna captive and frightening many of our heroes.[2]