Gaseous Form: Abyss seems to be composed of a living gas. She is mostly invulnerable to physical harm, although she can still be harmed by unconventional attacks. She can solidify her form at will.

Mind Alteration: Abyss possesses the ability to suggest ideas, and manipulate certain beings into acting the way she wants.

Essence Reading: Abyss also seems to have some ability to analyze life forms, as she was able to tell that Thor was of a mythic origin simply by looking at him.

Formerly New Avengers, A.I.M. (Advanced Idea Mechanics), Ex Nihilo, Avengers

Where Ex Nihli are creators/personifications of the potential for life, it could be construed that Abyss are representations of death - their natural antithesis. But given that Ex Nihil themselves are able to eliminate/prevent life and the fact the Abyss cannot be killed by conventional means, a more accurate assumption is that she is a representation of nothingness, void, the absence of life rather than the removal of it. Thus she too represents utter potential as all voids can be refilled. She may even be incapable of actually taking life as her primary means of attack and defense involve acting through others.
She may be the only Abyss left in the entire Multiverse, as Hank Pym found none at the Last Refuge of the Builders.

Formerly Savage Land; Avengers Tower, Manhattan, New York City, New York; Garden, Mars

Jonathan Hickman, Jerome Opeña

Builders (creators);
Ex Nihilo (brother, deceased);
Ex Nihila (sister, deceased);
Ex Nihili (brother, deceased);
Nightmask ("nephew");