Hades has skeletons in different military uniforms, guarding the halls of his Palace. These surround Percy Jackson, Annabeth Chase, and Grover Underwood when they are in the palace and would have killed them if not for Poseidon's Pearls.
- Main article: Skeleton Warriors
The General summons a variety of Skeleton Warriors to kill the Hunters, Zoë Nightshade, and Bianca di Angelo, but they chase after Percy instead. Bianca is able to kill one, and Nico di Angelo sends the rest to the Underworld before either realizes they are children of Hades.
Nico employs skeletons in rituals to call the spirit of his sister to speak with him.
When trying to escape the Underworld, Nico uses his power over the dead to put the skeletons he sees to sleep. However, this also causes him to become very tired. Near the end of the final battle he and Hades bring an army of skeletons to battle the Titan Army. Later, a group are constructing Nico's new cabin at Camp.
- With the exception of Atlas' skeleton warriors, most skeletons are not described as anything more than skeletons.
- They are seen holding many different weapons such as swords, guns and grenade launchers.
|Species:||Centaur | Cyclopes | Dragon | Drakon | Empousa | Fire-Breathing Horse | Giants | Gorgon | Harpy | Hyperborean Giant | Ichthyocentaur ||
|Friendly Monsters:||Argus | Blackjack | Briares | Chiron | Don | Ella | Festus | Gleeson Hedge | Gray |Grover Underwood | Hippocampus | Mellie | Mrs. O'Leary | Ophiotaurus | Peleus | Scipio | Tyson | Tempest|
|Enemy Monsters:||Agrius and Oreius | Arachne | Basilisk | Charybdis and Scylla | Chimera | Chrysaor | Clazmonian Sow | Colchis Bull | Echidna | Euryale | Geryon | Joe Bob | Kampê | | Nanette | Manticore | Medusa | Minotaur | Nemean Lion | Polyphemus | Sphinx | Stheno | Typhon | Scythian Dracanae|
|Neutral Monsters:||Carnivorous Sheep | Cerberus | Erymanthian Boar | Gray Sisters | Gorgons | Furies | Flesh-Eating Horse | Gryphon | Siren|