I took a step back, the sound of my hoof against the unseen surface below me echoing through the void, as the looming figure's horn lit with eldritch green flame. "wh.. who are you?"

The light cast by the flames revealed the face of an alicorn mare, a cruel smirk twisting her lips as her eyes narrowed. Shards of black crystal protruded from her horn, each one emitting a faint trickle of smoke, and her spread wings reflected the light of the green flame, revealing them to be made of crystal or glass as well. "What.. you don't recognize me? I'm hurt, Skydreams." I squinted, then my eyes widened with shock as realization dawned on me.

"That's right. I'm you, little pony." She tossed her mane and laughed mockingly. "I am the potential you have within. I am the power that is yours for the taking." She gestured with a hoof at the amulet affixed to the torc around her neck. "You have but to channel your magic through this, and all your heart desires shall be there by your word. Power! Adoration! You will no longer be a struggling mare among many in the underutilized army of a princess" she spat the word as if it had burned her tongue "but a goddess in your own right! Anypony who has even slighted you will now grovel before you, begging for your mercy! And" her smirk grew, and suddenly white spires and arches began to rise out of the void "you can tear that wretched city from the sky."

——-

I imagine Nightmare Skies as sounding like Megaera from Hades.