List of characters in the Camp Half-Blood series
Keres - A bunch of battlefield spirits of famine and disease that feed on violent deaths. They reside in the Underworld and support the Titans but do not assist them in "The Last Olympian." In "The Demigod Files," a bunch of them attacked Percy, Thalia, and Nico where one of them poisoned Percy. Lucky for him, Bob the Titan managed to heal him.