Hades

Near to the entrance to The Crystal Empire containing tracks that connect Ponyville to The Crystal Empire and has a hidden shed underground, The Pony Express is immobilized when its water tank is empty and broken down. A black train appears and offers to take frightened ponies and fillies to King Sombra's himself, which he accepts. However, once they were in his boxcar, the black locomotive reveals his true form as The Hades Express or Hades, having tricked all pony civilians. And The Hades Express or Hades The Evil Train is truly a living engine that is enfueled by King Sombra's Dark Magic. He reveals his intentions to keep ponies and fillies in Ponyville to keep The Main 6 left behind and halt the delivery of justice, so the only thing that could be delivered were King Sombra's slaves and crystals. Twilight demands him to let them go, only for Hades to scare The Mane 6 away from the tracks, leaving them frightened and since The Pony Express was broken down.