Abyss is the final boss of the Marvel vs. Capcom 2 style of the fighting video game, M.U.G.E.N Trilogy. He is located at the tenth and final stage of Arcade Mode. He comes in three different forms: The Armor of Erosion, the Guardian and the Abyss, himself. Kan Tokumaru provides the role of all the three forms for Abyss.
Abyss is a legendary creature, forgotten by time and believed to be just a fairy tale. Born in ancient times, in an era where magic prospered, Abyss is a forbidden weapon sealed away in an underground temple where it spent untold centuries in a deep sleep. When its resting place is disturbed, however, Abyss and its unparallel power begins to awake. Its rise releases hideous waves which mutates all marine life, and cursed winds blowing from the seas which kill any animal or plant life on land. Abyss is something akin to entropy incarnate, a fabled monstrosity that would bring the world back to primordial times, killing all life in the process.
- Form 1 - The Armor of Erosion. Due to its current incomplete state, Abyss dons the "Armor of Erosion", a massive black suit of armor built by Abyss' creators in order to control its immense power. Abyss fills the armor with green liquid in order to control it, jutting two large green horns out of the top of the mask. Although the armor was made to restrict its power, Abyss still exerts an incredible amount of strength from within it.
- Form 2 - The Guardian. A transitory form, Abyss creates it as a protection while it goes through the process to reach its final form, after being released from the constraints of the armor. The Guardian is a humanoid-shaped being made entirely of a green substance, capable of turning its hand into an arm cannon to attack relentlessly with flames and laser beams. The Guardian's body is only a fragment of Abyss, separate from its real self.
- Final Form - The Abyss. Abyss takes this form after restoring its full powers. It appears in the form of a giant, four-legged demon made up of dripping red substance, displaying a sharp-toothed face which melts away to be replaced by a new one (or three), and large tentacle-like limbs. Now wielding god-like powers, Abyss proceeds with its ultimate goal: to devour all of existence, intent on returning it to the primordial sea from where it originated, the "Sea of Genesis". This is demonstrated after losing the match, as Abyss will strike the downed character, launching them into the air and leaping at them to eat them whole, after which it licks its lips.