One day, a small filly by the name of Pink Sunshine falls into the underground. She eventually falls into the hands of Sans, a laid-back Skeleton who likes to make bad puns. Through their adventures, they'll Fight Flowey, explore hotland, buy Spider treats, and overall have a good time.

Or maybe not.

Undertale/MLP Crossover. It also contains MASSIVE Spoilers for Undertale, and I don't own any Undertale characters. It takes place after the yellow human falls and before Frisk. And the cover art was done by me.