Starting at 18th level, you can spend 6 sorcery points as a bonus action to transform yourself into a shadowy form. In this form, you have resistance to all damage except force and radiant damage, and you can move through other creatures and objects as if they were difficult terrain. You take 5 force damage if you end your turn inside an object.
You remain in this form for 1 minute. It ends early if you are incapacitated, if you die, or if you dismiss it as a bonus action."
Invulnerability: This means that you can cast a spell and enter an object in the same turn to get the benefit of full cover.
You may still have resistance against radiant damage being aasimar.
In practice, you are invulnerable.
I back to the fight every turn: You can wish for duplicate Regenerate spell that means that you can't be defeated by damage for 1 hour. (Regaining 1 hp per turn, you back to fight each turn even if you are reduced to 0 hp)
Long range and reliable damage: Distant spell for Insect Plague for 620ft range that can be insane combo with Aasimar Racials.
Empowered 5d10 + extra damage equal your level that ignore cover as your most reliable damage spell.
Spellcasting Superiority: Subtle Counterspell (Always win a counterspell battle) and Distant Spell for long range spell. You are a beast on spellcaster battle.
Incredible mobility: Subtle/Distant Dimension Door and Shadow Walk for insanity "Surprise Mother ****er, I'm here!"
I'm here, mother ****er!
It's just insane effective.
You can also apply twin spell on Simulacrum (Via wish) for still more power.
THE BLACK HOLE...The Shadows will devour you!
Step 1) The Shadow Lord and His simulacrum with Darkness Spell and Umbral form moving through objects.
It's literally total cover and block line sight (Countering hard "you must see the creature" spells and effects).
Step 2) Move out of the enemy's spell range. Keep always out of true sight spell's range (120ft).
The Shadow Lord casts Distant Empowered Dark Star for 300ft range (Casting via Subtle Wish). The enemies can't cast spells with verbal component and It's blind and deaf.
The Simulacrum casts Distant Reverse Gravity for 200ft range. The enemy can't move.
The enemies are imprisoned on reverse gravity, blind, deaf and can't cast spells with verbal component.
Also, taking Empowered 8d10 force damage +20 (Aasimar Ratials) per turn automatically.
Step 3) Move inside walls again to get total cover again.
It can literally desintegrate all party in a single turn.
It can't be countered... How?
Only sorcerer's subtle spell can avoid it.