Episode 13 Do Princesses Dream of Magic Sheeps? Is when would show in the show on July 11. On the wiki it said

"Princess Luna enlists the Mane 6 to help her track down the Tantabus, a magical force that threatens to turn everypony in Equestria's dreams into nightmares."

Is he the reason why Luna became Nightmare Moon and if so are there more out there or a some sort of stage of turning into one.

4513666
Actually no. In the episode, we learn that Luna created the Tantabus herself to punish herself for her time as Nightmare Moon. The dark force fed of her guilt and fear and became so powerful, it could escape her dreams.

4635876 it kinda to late to tell me that already

4636242
Who cares? XD I did it anyway.