Yourself and your doppelganger walk side by side down an unfurled red carpet stretched over a city road, hundreds of people lining the street.
Some kneel as if in prayer, some bow as you pass, and some weep. The houses behind the crowds are cracked and empty, the only signs of respite from the overbearing ruin and tear being the occasional flicker of a fire deep within. Shadows skitter around the edges of your vision when your gaze strays too far from the path.
The sense of animosity between you and your doppelganger is gone - she is an extension of you, and you her. A sum greater than its two parts.
A nearby human breaks loose from the crowd and rushes at you, sharpened stone in hand. As one, you both raise your hands, and a roaring flame extends from your palm to reinforce the mass of thorns your doppelganger spawns around your assailant.
He stares with hatred into your heart. The two of you reach into his mind, pulling at it as two dogs would a bone, before deciding that another mind that sees you as a goddess would be best. You play for a moment, sculpting as a child would a mass of dough, then release him. He flees back into his line, and prostrates himself before you.
You finish your walk at your destination - a large, nearly fifteen-foot-fall shadowy figure, overlooking a large town square whose bottom  is obscured by fog. Two heads protrude from his neck - one barking and snapping at the air, and the other sitting in silent contemplation. You both kneel in subservience as it turns around and faces you, one face appraising you each.
It opens both of its mouths, and two voices fill the air.
One, snapping and screaming, salivating like a rabies-infected dog. "CRUSH THEM ALL. BREAK THEIR MINDS AND BODIES. INFINITE POWER."
One, meditative and soft-spoken. "The respect and freedom you have always wished for can be yours, my child. Do what you wish. Be you who you wish. You need merely pay one price."
Four tendrils emerge from the sides of the being and lift both of you in the air, directly in front of it. Two simian heads peer at you, one nearly crosseyed with rage and the other silent and contemplative.
"Everyone else."
The fog clears from the town square to reveal a heaping mountain of corpses and several enormous stone pillars. Muirthum Earthforger is mostt prominent, his face contorted in agony and betrayal, hands forever locked in a desperate reach for freedom. Two beings you recognise as your parents - forms come and go, but familial bonds stay. They remain in a docile state, eyes closed in heartbreak and acceptance.

The fog lifts over the town square beneath these pillars. Fire and brimstone mark an endless hellscape - those few people that remain alive are either being tortured or chased by roving packs of demons or leading those packs against their kin.
More power than you thought you could comprehend surges through your body, urging you to reshape reality. At a whim, you and Nix could make this city into a jungle. You could live forever, take whatever pleasures you wished, create a plane or two as a side project.
You turn back to the pillars.
Anything except undo the past.