Monsters are creatures that appear in the different mythologies.
Monsters are considered offshoots of gods or cursed beings that terrorize, fight, and often kill demigods and heroes. Monsters are "archetypes," born from the Chaos and Barbarism that always exist in the Western Civilization. This means that they are purely abstract entities and will merely reform in Tartarus and come back whenever they're physical form are destroyed. However, not every monster when killed goes to Tartarus. In the case of satyrs, when killed they will be reincarnated as something else in nature, like a plant of some kind, though it should be noted that satyrs are nature spirits, which might be different from monsters. Monsters often serve as minions of evil and cause trouble for Olympus. Normally, since they can't hurt the gods directly, they go after their demigod children instead. However, some monsters such as some Cerberus, Pegasus, and the Furies serve Olympus. There are other monsters like the Cyclopes, dragons, harpies, Hellhounds that work for Olympus or run wild on their own. When some monsters are killed, they leave a trophy behind (called a Spoil of War) in the form of parts of its body, its clothing, or some kind of armament.