- "Meet the same minion who destroyed the Core of Light - and will do so again! Meet the beast who sent Eon to his well-deserved bodiless OBLIVION! MEET... my Hydra!!"
The Hydra, also called Hydragon, is Kaos's four headed dragon in the console versions of Skylanders: Spyro's Adventure. It is the most powerful of all of Kaos's Minions, and didn't make a full appearance until the last battle between the new Portal Master and Kaos. It was most likely used as a last resort for Kaos.
- The Fire Dragon head can conjure a Fire spell that summons moving fireballs that spawn mini volcanos.
- The Life Dragon head can conjure a Life spell that summons green energy orbs (which are sometimes accompanied by red bug-like creatures that can be defeated to remove orbs).
- The Undead Dragon head summons lasers that move throughout the arena.
- The Water Dragon head summons flowing water and a large number of Doomsharks. If you go between the sharks and avoid damage, you will regain 11 health.
When he was losing his second attempt to destroy the Core of Light, Kaos released his Hydra into the battle and it was powerful enough to successfully destroy the Core; its destruction was what triggered the events of changing Master Eon into a spirit (though he survived the blast), caused Kaos's castle to go flying back out of control, and banished the Skylanders to Earth.
When the new Portal Master and their Skylanders finally confronted Kaos face-to-face, the evil tyrant summoned his Hydra to aid him in the battle. Harnessing four of the main elemental classes, the Hydra proved to be a powerful opponent though it can't be fought directly due to a magical barrier that surrounds the arena. After Kaos is defeated, the Hydra withdrew back into the darkness and was never seen again.
- The Hydra's shadow can be seen above the Core of Light in the cutscene right before the Core is destroyed.
- The Hydra bears a slight resemblance to Dungeon & Dragons' Tiamat.
- Each of the Hydra's heads are the same elements as the Eternal Sources Kaos used during his battles against the new Portal Master when he attempted to keep the them from claiming the Eternal Sources for the Core of Light.
- The Wii version of the battle is the most difficult, because Kaos recovers health when all of the Evil Minions are defeated.
- According to an infograph about the Skylanders franchise, Kaos rented the Hydra from the Doom Valley Evil Nature Reserve as part of his plan to destroy the Core of Light.