Pitch Black is not your ordinary, everyday stallion. For starters, he can't exist in sunlight. When ever he does get caught in even the tiniest bit of light from the sun, he vanishes. He comes back once the sun has set.
Nopony knows where he goes. In fact, nopony really notices him much. He always stayed indoors when it was day. However, when it was night and everypony slept, he had most of the run of the town.
That's how life for him went. Hide in day, wander through the streets of Ponyville at night. When Nightmare Moon came and decided to bring everlasting night, he was overjoyed! However, the sun did come back, making him vanish into thin air once again. He still came back the next night, but how is he supposed to live like this? His parents died recently, and the day just seems to drag on, and on, and on...