You went on a genocide route in Undertale, and, as usual, you got ready to fight Undyne The Undying. But, as you approached the spot where the fight would start, it was strangely empty. You searched the area to find out if you made a mistake, but you found nothing. Then, your computer froze, and you blacked out.

It was cold and damp. Something wet was tapping your face, and when you woke up, you felt very small. You heard a growl.

"So, it did work... Surprised to see me? You aren't so tough at all, now that you're in OUR world. And that size... You're the real monster. Alphys found a way to transport a mind through the screen or whatever. Makes you really small... What matters is this is REALLY you, and you aren't getting away."

She presses her foot on your face

"You should be grateful I don't end you right here. But, in this state, you won't be much of a threat. You'll be a toy for the whole underground. Small and weak... Too little to resist us. It suits you. After all, you did kill so many monsters."

She looked angry and smeared her soles on your face, clearly not happy about your presence.