After a stellar celebration of the anniversary of Luna coming back, she starts having nightmares more often, and so has the rest of the Mane Six and their other friends. Though the Tantabus is dismissed immediately, and the Nightmare Forces that turned Luna into Nightmare Moon are not responsible since they were cured of the darkness Pitch reaped on them thanks to the Mane Six, they tie this to a powerful spirit similar to the Tantabus but far more frightening, in the form of the last Nocnitsa in Equestria known as Tenebrae, which is a nightmare spirit that Luna defeated long ago, and yet disappeared before she could seal it away as it adapted to her powers. After looking for clues, it's revealed that it was previously defeated already by another one of Starswirl's past students, Zodiac Cloud, who lives in a hippodrome in Hollow Shades turned into his legendary Temple where he helped educate to prevent Pitch's oath of haunting a future generation come true by having a hoof in his remembrance, as he had cured the Taraxippus that haunted him by discovering it was in love with him because it was born from a pony that died from bullies accidentally after a long time of loneliness, and married her and had kids before they were killed by Tenebrae herself, until he sealed her into a prison in his educational realm, the Uncanny Valley, which is a realm that combines both the real world with the subconscious to allow easier fighting against internal and external forces combined, and though the setting has the same physiology as a dream like nonsense, surrealism, and so on, it provides a good place of training such as lucid dreaming, and fighting against mind domination or illusions, or even counter-attack. As the result of Bishop Dipper's terrorism with the Taraxippuses as the new Pony of Shadows, he has ended up freeing Tenebrae from her prison within a dreamcatcher called the Cross of Dreams which is destroyed following her freedom, as it seeks to be the new Pitch Black and free the Taraxippuses to help fight to make fear both mental and outer to gain more strength. When it gets stronger every passing night, the Lodgers, who end up experiencing Tenebrae's influence upon arrival, must do what they can to save their Equestrian friends from this haunting threat, by trying to find the Cross of Dreams' creator, the Alicorn of Dreams Princess Phantasma.
- Twilight:... What? NO! I WON'T LET YOU TAKE ME!!
- Tenebrae: (In Twilight's voice) It's too late! And all I learn about you, you are the PERFECT host! Celestia? Luna? Rarity? Starlight? STARSWIRL?!? They are nothing compared to you! You, have a LOT on your mind that I can take a LIKING to you, as the PERFECT host!
- Twilight: NO! GET OUT!! (She fired a blast of magic as it only faded through her and struck her after appearing from behind) UGGH!
- Tenebrae: (Cackles) You are SUCH a good story and GOOD potential. You take shots from those who tell you what you can really be, and even yourself! You are stressful, prone to a good challenge, has a lot of wishes and personal dreams... AND YOU HAVE FEARS TO EXPLOIT! (Twilight was horrified she got this knowledge) The abandonment of not just Celestia, your surrogate mother, or even losing her... And even the same to your friends, or worse... DESTROYING IT! (She saw visions of her dark future with Sombra, her snap in the movie, Pitch Black's encounter, and many others as Twilight couldn't take it)
- Twilight: ENOUGH! (She exploded in magic) I WILL NOT LET YOU CONTROL ME! I HAVE THE MENTAL DEFENSES TO KICK YOU OUT!
- Tenebrae: (Cackles)... Here's a real kicker: I'm not using the mental spells that you need defended from. I am only visiting you in your subconscious, like in a dream. I am not harming you and therefore I can get past your occlumency, as it can't perceive me as a threat because I am not doing any harm, even if I wanted to. But you? You feel like you need something to let out.
- Twilight: STOP WITH THE MIND GAMES!!!
- Tenebrae: Well, am I wrong? You're scared of a LOT of things. Everything you love and care about walking out on you or being destroyed, OR destroyed by you, just, like, Celestia! And I can break you without even trying, and without knowing I'm doing it. It comes with being a nightmare spirit, really.
- Twilight: I REFUSE TO HEED TO YOUR TRICKS!!!
- Tenebrae: Well, ask yourself this: How long will your friendship last? How long before they turn on you for a far worse mistake than the theft of a magical relic, or a harmful mistrust. And given how much you are, I know there's ONE likeliness that can destroy you indefinitely.
- Twilight: You're bluffing! There's NOTHING-
- Tenebrae: Mayhem made it seem possible, and so can I! (Cackles as the setting changes)