Ouroboros

Ouroboros (ウロボロス) is the final stage of Mega Man ZX Advent. It is the ultimate Biometal, created by the full awakening of Biometal Model W. It emerges from Master Albert's hideout from the Undersea Volcano.

Characteristics
Ouroboros is the result of all fragments of Model W awakening and merging. The result is a colossal Biometal resembling the eponymous symbol of a snake biting its own tail in a clockwise manner. It has a golden head with red eyes and a segmented white body with glowing red power lines and proportionally small vertical wings.

The interior of Ouroboros is drastically different; the first half of the stage is made of large Model Ws mashed together in a very disorganized manner. Glowing red gems are prominent in the fragments, and the background also includes a giant mechanized red sphere connected to enormous cables. Deeper areas display an entirely different aspect, with the background becoming riddled with gigantic red tubes pulsating like arteries with an intense orange light emanating from below.

While Ouroboros itself does not manifest a personality, it is indicated to contain incredible power; Master Albert claims that the spirits of everything Model W devoured live on inside him, giving him the ability to control all life with the real A-Trans; he demonstrates this by not only transforming into Pseudoroids, but also manifesting their actual personalities, something that cannot be accomplished by Model A's A-Trans.

History
Following the revelation that Master Albert is the creator of Model W, the Sage Trinity member escapes Legion and begins to retrieve Model Ws everywhere, gathering them all in his base within the Undersea Volcano. Ouroboros is mentioned for the first time when Model A's final cipher is unlocked during a fight between the Mega Man Model A (Grey/Ashe) and the Mega Man Model ZX (Vent/Aile). The cipher reveals the full extent of Albert's plan to the two Chosen Ones, mentioning that the one who wields Ouroboros will evolve beyond "the mere fusion between man and machine". The two Chosen Ones join forces and begin to investigate new leads.

The Mega Man Model A eventually finds Albert's hideout, but the ex-Sage Trinity is slain by Prometheus who, along with Pandora, hates their creator Albert for forcing the two into centuries of servitude. However, the two fall for Albert's ploy, fainting as their sheer hate is absorbed by all the Model Ws, providing the data needed for their full awakening.

Albert reappears in a new body, revealing that Prometheus had taken down a decoy as the fragments merge into Ouroboros, destroying the hideout and emerging from the sea. The Model A Chosen One is forced to escape, leaving Prometheus and Pandora behind. An endless swarm of Mavericks emerge from Ouroboros, wreaking havoc throughout the globe as Albert carries out his plan to make a new world.

However, Ouroboros is boarded in the sky by the Guardians, who joined forces with the Hunter's Guild with the approval of Master Thomas to stop Albert. The Guardian Base crashes into the ultimate Biometal, allowing the Model A and Model ZX Mega Men to infiltrate it. Though Aeolus, Atlas, Thetis and Siarnaq attempt to stop the Mega Man Model A, the four are held back by Vent/Aile, who demands them to hand over their Biometals while the Model A Chosen One moves on to confront Albert. The Mega Man Model A and Albert engage in a bitter battle, with the former being victorious despite Albert unleashing the power of the ultimate Mega Man. Albert dies and Ouroboros explodes in the sky, vanishing in the sea without a trace. The Mega Men, the Hunters, and the Guardians manage to escape, but Model Z is lost in the process.

Structure
The game map separates Ouroboros into four segments.



Ouroboros 1
The first section of Ouroboros is relatively straightforward; the main obstacles are Reflector Cannons, Sawoods, Galleon Hunters and Galleon Shockers. There is a short stretch of solid blocks over a series of spikes near the door to the next section. The blocks may be destroyed by powerful physical attacks such as Buckfire's Meteor Kick, Bifrost's Ice Bite or Atlas's Megaton Crush.

Ouroboros 2
This section is composed of a corridor leading to a pair of identical rooms with four teleporters each. This is where the player has a rematch with the Pseudoroids of the game. They are arranged in the following order for each room (left to right, top to bottom):
 * Room #1: Vulturon, Rospark, Chronoforce and Buckfire.
 * Room #2: Argoyle & Ugoyle, Hedgeshock, Bifrost and Queenbee.

Defeating them all is mandatory to proceed to the next section.

Ouroboros 3
This section has much more hostile obstacles than the first, being characterized by red blocks and spikes placed near pits and spike beds. The red objects may be destroyed, but those regenerate after a few seconds and the player will lose a life if the character remains on the same spot as the regenerating object. The quantity increases as the player advances, while additional hindrances are provided by Reflector Cannons, Meteor Threshers, Galleon Spiders, Burners and Caroms.

Ouroboros 4
This is the final area, but also the shortest one as it amounts to a short stretch leading directly to Master Albert's throne room. A cutscene plays where Vent/Aile holds back the evil Mega Men, allowing the Model A Chosen One to face Albert himself.

Trivia

 * The awakening of Ouroboros through the hatred of Prometheus and Pandora harkens back to Serpent using the hate of Vent and Aile to awaken the Model W core in Mega Man ZX.
 * The rooms which lead to the Pseudoroid rematches display a giant glass painting in the background with the image of two women reaching out to Albert's crest; one appears human, with long blonde hair and the other has the head of a Galleon. The blonde one bears a strong resemblance to Ciel, while the other one bears a strong resemblance to Iris.
 * The power to control all life through Ouroboros may be a reference to Dr. Weil's skills in Reploid resurrection.
 * It is also a resemblace to Ragnarok, Weil's satellite from Mega Man Zero 4, the remains of which Weil is fused with.
 * The Mega Man ZX series appears to follow a theme of snakes in antagonistic roles, starting with the Giga Aspis and Serpent in the first game and culminating with Ouroboros in Mega Man ZX Advent.