The abyssal arm is a prosthetic (unbreakable) left arm, it connects at the shoulder but in return you get the following affects.

Magical blessing: the prosthetic arm grants 3 abilities, they are as follows.

Telekinesis. As a Bonus Action, you can telekinetically push or shove one creature you can see within 60 feet of yourself. When you do so, the target must succeed on a Strength saving throw (DC 18) or be moved 15 feet toward or away from you.

Inhuman Endurance. While attuned to the arm, you gain a +2 to both your Constitution score and your Constitution saving throws. Additionally, you no longer need to eat, drink, or sleep while attuned to the arm.

Enhanced Athleticism. You gain Advantage on any Dexterity (Stealth and Acrobatics) checks, as well as Strength (Athletics) checks you make.

Notes: Utility, enchantment