The Ultimate Being is the final boss of the vide game Parasite Eve. A horrible mutated humanoid creature of apocalyptic intents, its very existence caused living beings to self-combust and thus made it a danger to the entire world. The Ultimate Being is the child of Eve, who managed to conceive the monstrosity in order to pave way for the final battle.
Taking the form of a groteque baby with a tail and wings it attacked with a kind of psychic shockwave before mutating into a larger form.
In the second form, the Ultimate Being developed telekinetic powers and became less infant-like in design, more closely resembling a dark angel but with the likeness of a pre-teen.
After a while, it reaches its third form of a seemingly human teenager as it detatches its wings and becomes more alien, gaining the ability to fire energy from its tail.
After this form is defeat the Ultimate Being mutates into its mature-form and becomes a savage fighter capable of numerous attacks.
After the mature-form is defeated the Ultimate Being mutates a final time into a truly alien being, being so powerful its defeat was only made possible by the use of special bullets infused with Aya's DNA.
However even when badly injured the Ultimate Being pursues Aya through the ship, until she sets the ship to explode - seemingly killing the Ultimate Being in the process.