Hello! I've recently became hooked on Undertale so I had to make a crossover.
Summary: Lily does the unthinkable after hearing that Voldemort was after her son. She turns him into a monster.
Pairing: Papyrus x Sans x Harry (I'M GONNA MAKE IT WORK, DAMMIT! SANS X PAPYRUS IS MY LIFE NOW!)
I hope you enjoy!
HPSPHPS

Lily ran. She didn't care what her husband said. What Dumblefuck said. She refused to let it happen. To let Fate send her son's life spiraling down to hell. Fuck. That.
So, what was Lily gonna do? Running will result in being caught. Hiding will result in being found. She thought long and hard. Then she remembered a voice.
"Well, if you need anything, and I mean anything, just find a dark cave with a seemingly endless hole. There are many opening to our world. It's the least I could do to repay you…"
And that what Lily did. After scribbling a note and wrapping her baby in the softest and fluffiest blanket she could conjure she set off to find the cave. She looked in every cave she saw, but none had a hole deep enough. After hours on end of looking, the sun began to rise. Her husband would be up soon. If he saw her and the baby gone, he'd contact Dumbledore, who would find them and drag them back. She couldn't afford to give up.
Finally, she came across a cave in a mountain. She felt a strong magic in it. Relief flooded all of her emotions. She couldn't stop herself from running into the cave. She ran for abut half an hour before she halted. In front of her was a huge, gaping hole. It seemed endless, just like her old friend had said. She couldn't think of anything else to do, so she yelled down into it, praying to be heard. "Toriel! It's me, Lily! Please, I need your help! A prophecy has cursed my son, and I can't let it ruin his future! Make him yours, or anyone's! Just make this burden invalid!" She stood, waiting for a response, but nearby cracks of apparation were heard, and she couldn't stay long. She looked downed at Harry. He was still sleeping peacefully, unaware of what was happening around him. 'He'll survive…' Lily thought, hugging her son close and kissing his forehead. 'He'll survive…'
"Mommy loves you… She always will…" Lily told him. Just as she heard footsteps coming closer, she threw Harry down the hole. "Goodbye!" She yelled down. Without even looking at the shocked faces behind her she apparated. No need to stay there any longer then she had to.