Equestria Expanded Universe #5.5
Ponytropolis #5.5
2017 Nightmare Night Special

Fed up with trying to lure Twilight in her dreams, Nightmare tries something else; possessing one of Twilight's closest friends to get her to give herself over willingly. When Twilight refuses, Trixie must overcome her fears and Twilight must face Nightmare again if the blue mare is to be saved.