Spike is left behind when the crystal empire celeabrate the defect of Sombra. He was told by Twilight that her and the other Saved the empire and he was just there for carrying bags for Rarity. When they left he went into rage as he breaks everything the Twilight owns but after rage quiting he went to sleep but was waking by ink like hands that grabbed him and enter him the mirror he enter a year ago.

He gets send to the WasteLand, while another ink creature goes out to stole the crystal heart. Spike meets many version of his friends and ponies he knows. Soon he meet some mixed horror version of them take tries to kill him. Spike must found a way to get home and get the Crystal Heart back.

(Also I got the idea of this from electricdragon505)