If it wasn't already obvious, "Hearth's Warming Tail" was based on the classicCharles Dickens novel "A Christmas Carol". In the book, Scrooge, or Starlight Glimmer in our case, has a business partner named "Jacob Marley". Apparently the original idea for the episode actually included him, played by Discord.
Maybe some day we will see what the outline called for, but that's what our fanon is for! How would you have treated a ghostly Discord bothering Glimglam?
Thanks to Nick for sending it!