My Little Pony: Friendship Is Magic (2010)

S05E13 Do Princesses Dream of Magic Sheep?

After the enigmatic Tantabus breaks free from Princess Luna's subconscious, she realizes she must act swiftly to contain it. If she fails, the creature could transform the dreams of all ponies into terrifying nightmares. With time running out, Luna embarks on a quest to confront her fears and reclaim control over the dream realm before the darkness spreads.