Mettadom

so basically you were walking around through the core with your [INSERT WEAPON] and [INSERT ARMOR] through the underground as you battled monsters as you go further into the underground you passed snowdin town all 3 puzzles and you met a few people along the way like papyrus sans Tories and more and so you make it pass the MTT resort with your [INSERT SOUL] and then as you went through you made it to a stage....

METTATONS STAGE ---------------------------------

now you were expecting mettaton but then you saw a women who looked like Mettaton she had the same hair style as Mettaton and outfit but she had black makeup and a smirk and her ass was big able to engulf your legs and crack the ground beneath her and her thighs could easily take someone out and her tits could smother someone to death....DEATH BY GLAMOUR

Mettadom:well hello dear she said in a zesty flirty way your looking for my brother well he's been on vacation so I'm covering for him so your another dancer it's nice to have another one she giggled

it was Mettadom, Mettatons sister. She is a  android designed by Alphys, appearing as a tall, slender pop star with pale "skin" and greasy black hair that covers her right eye. Her features a pink chest plate with speaker details, black shoulder pads, a narrow metal waist, and long legs ending in pink high-heeled boots Face: Pale with metallic segments around her left eye, often depicted with a charming yet narcissistic expression.Chest & Waist: A pink, heart-shaped chest plate featuring a speaker and dials. Her narrow waist holds a "heart-shaped core" locking mechanism.Limbs: Segmented robotic arms ending in pink gloves and long, black-clad legs.Style: Heavily inspired by 1970s glam rock (resembling David Bowie/Ziggy Stardust), focusing on flamboyant, androgynous, and "fabulous" fashion.Metamorphosis: This form is triggered when the switch on her back (as a rectangular box) is flipped, revealing the humanoid form.