Hydra

Hydra (妖蛇, Yōja, lit. Supernatural Snake) is the main antagonist and a non-playable boss character in Warriors Orochi 3. Its appearance caused many deaths within the dimensional realm and it is depicted as an unstoppable beast. Characters throughout the game's script may alternatively refer to it as the "Giant Snake".

Role in Game
Orochi created the dimensional world with the desire to destroy himself. As such, his will for ruin remained deep within the dimensional world's consciousness. When humanity killed Orochi a second time, they unknowingly began the catalyst for triggering the world's will to seek ruin. Since Orochi's body is tied to his world's wishes, his raw power eventually manifested itself to take shape within the dimensional realm as a thoughtless and crazed giant of destruction. This form of the world's will is dubbed Hydra by characters. Though he shares humanity's wish to slay the beast, Susano'o initially blames humanity's incompetence for its existence and subsequently refuses to associate himself with them.

As a source of seemingly limitless power, it can endlessly revive itself and the serpent forces. Its appearance into the dimensional world alone fuels Kiyomori's resurrections and decimated humanity in the original timeline. Thanks to Kaguya's intervention and Da Ji's eventual allegiance, the coalition for humanity is able to return to a past before its "birth" into the dimensional realm.

Though unable to prevent the Hydra's birth, the coalition continues building their forces and obtains the firepower they need to defeat it. Once they slay each of its eight heads, Hydra reforms itself as eight Orochi figures. It assumes a final Orochi X form when these eight clones are defeated. While it is called Orochi X by the game's script, the immortals stress that this form of Hydra is a god of destruction and not Orochi himself. It only seeks to devour the world in ruin.

Hydra's final defeat at New Koshi Castle and the time distortion caused by the coalition's countless time traveling causes the dimensional world's immediate and unavoidable destruction. Ultimate retcons this by having the story follow the good ending instead.

Fighting Style
As an eight-headed serpent beast, it mainly breathes fire on its targets. The fire breath is multi-hitting and unblockable. Sometimes, it may also spit out arcing fireballs that explode upon landing. The only way to defeat one of its heads is to fire at it with the Yashiori. The Orochi clones it creates keep Orochi's respective movesets (Orochi and Orochi X) separate.