Abyss, known as the Armor of Erosion, is the antagonist in Marvel vs. Capcom 2: New Age of Heroes. He was responsible for a mysterious wind that spread across the world, killing plantlife in its wake. This phenomenon prompted numerous heroes and villains to band together and investigate. He's something akin to entropy incarnate, a fabled monstrosity that would bring the world back to primordial times, killing all life in the process.
Abyss's true form is apparently that of a large glowing sphere that hovers around in the background. Abyss changes into three different forms when fighting.
In the first stage of the battle, the metal sphere surrounds itself with a giant suit of armor which is slow moving with powerful attacks. The fight takes place in a large temple like structure, presumably underground.
After this form is defeated, the armor melts into the floor and the temple crumbles, leaving the fighters standing in a green pool of slime. The Abyss sphere floats in the background as the second form reveals itself: a small green humanoid capable of creating paralyzing bubbles, shooting fire and energy beams, and sinking into the floor to avoid attacks.
After this form is defeated, the green slime turns red and a large demonic beast forms around the Abyss sphere. This third form attacks with powerful energy and sheer brute strength. If this form is defeated, the sphere apparently loses its power, and the cave and island the monster inhabits begins to sink.
Marvel vs. Capcom 2 has only one ending, which all the characters share. In it, the various fighters celebrate their victory over Abyss on the ship of the pirate Ruby Heart. This ending will vary, however, depending on which console the player is playing it on: on home consoles the characters that are available in the beginning celebrate, whereas in the arcade version, more characters are shown with a few changes to some scenes. At the start of this sequence, Ruby is seen holding Abyss's cracked sphere, which she drops into the ocean, and it sinks into the depths.