A dark creature made of shadows appeared in a quite strange cave, his name is Arachno. Because of the villains who all tried to attack Equestria, he revived. However, his only weakness is alicorn magic, and unfortunately for him, the four princesses of Equestria are alicorns. His only hope of success is to steal the body of one of them to be protected against that magic. But first, he need to corrupt one, and there is nopony better to corrupt than the innocent princess of friendship.
After season 6 but before season 7
And gore just in case
I thank 0_0 for editing my story