Asriel was sitting at the flowers, where Chara was buried under, waiting to become that wretched flower again. Before he could become that flower again he was stabbed an unknown assailant who said that he won't die and he'll be transported someplace else that could help him. After waking up in a small clearing in a sinister looking forest he finds a way into a small town inhabited by ponies that are like humans but different. He befriends three little fillies who decided to help him the best they can. They eventually take him to the Mane 6 to see what they can do to help him get home. Asriel will learn the magic of friendship and be able to go back home. Little do they all know is that Asriel will be able to reset the entire timeline with this type of magic.

Undertale and My Little Pony crossover. Enjoy!
Info on sequel here: http://www.fimfiction.net/blog/695488/lets-talk-about-my-undertale-sequel