Keres

Keres are battlefield spirits of famine and disease that feed on violent death. They live in the Underworld and support the titans, but didn't directly attack Olympus.

The Demigod Files
In Percy Jackson and the Sword of Hades, Percy, Thalia and Nico are ambushed by a group of Keres, and Percy is poisoned by one of them, and would have died if Bob (Iapetus) did not heal him.

Powers

 * Keres feed on death
 * Have deadly poison that only a gods', or titans', powers can heal