The South Park guys have been very critical of Seth MacFarlane and Family Guy over the years. In one scene, in the Blockbuster store, the movie Ted, also a Seth MacFarlane product, can be seen playing on a TV in the background.
Mr. Garrison is dressed up as the main character of Drive (2011).
When iPad version of Stan is captured by the burglars and questioned about his friends he admits their names to be Bruce, Tony, and Kurt. Bruce Banner (Cartman) is the Hulk, Tony Stark (Kenny) is Iron Man.
This episode was a spoof of "The Shining"
The title is a reference to Nightmare on Elm Street