Your Strength, Dexterity, Wisdom, and Charisma scores all increase by 5, to a maximum of 20 for each.

The Demon Has True Sight.

Your ancient heritage grants you inherent understanding of infernal, as well as two other languages of your choice.

One humanoid that Demon Lord can see within 5 feet of it must succeed on a DC 20 Charisma saving throw or be possessed by the Demon Lord; The Demon Lord then disappears, and the target is incapacitated and loses control of its body. The Demon Lord now controls the body but doesn't deprive the target of awareness. The Demon Lord can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, including gaining access to the target's knowledge, class features, and proficiencies. The possession lasts until the body drops to 0 hit points, The Demon Lord ends it as a bonus action, or The Demon Lord is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, The Demon Lord reappears in an unoccupied space within 5 feet of the body. The target is immune to Demonic Possession for 24 hours after succeeding on the saving throw or after the possession ends.

As an Archdevil, you resist necrotic, and cold damage.
immune to fire & poison.

you have the ability to step from one shadow into another. When you are in dim light or darkness, as a bonus action, you can magically teleport up to 120 feet to an unoccupied space you can see that is also in dim light or darkness

If a demon dies somewhere other than the Abyss, the body disappears with a flash of fire, dissolves into a pool of ichor and re-forms in the abyss, it is therefore not truly killed. However, a demon killed in the Abyss is dead forever; not surprisingly, that’s why demons tend to be more cautious in their dealings at home than abroad.