This story is a sequel to Equestria Ninja Girls Halloween Special
After the Beauty Trio's thief adventure with Sly Cooper, this year's Halloween was the most terrifying yet! And everyone had a blast! But on the eve of Christmas, Mikey, Pinkie, Rainbow Dash, the CMCs, and Aria entered a portal summoned by a strange key that the siren had, only to find themselves in terrifying new forms! Where were they and why did they become monsters? They meet scary friends and horrifying enemies, will they make it back home in time for Christmas? Find out on Equestria Ninja Girls: The Nightmare Before Christmas: Oogie's Revenge.
Disclaimer: Neither Darth Wrex, nor I own Equestria Girls, Teenage Mutant Ninja Turtles (2012) or Nightmare Before Christmas.