The Hydra King is the final boss in the Water Temple.
The Hydra King is invincible to start the battle. His area is filled with Water Guardians which respawn, and 3 Hydraeks. All 3 Hydraeks must be killed in order to make the Hydra King vulnerable. He can be lured out of the water so that melee fighters can easily surround him. He will summon several Tentacles to attack the heroes. He also casts anti-magic shell on himself.