How do you give a show that's been running for 25 seasons some extra life? You get a director like Guillermo del Toro on board and set him loose on the couch gag.
This epic, grisly tale is undoubtedly one of the best special guest creations in the show's long history, and, unlike the others, it starts well before the couch and has so many scary movie, pop cultural and past Simpsons references in such a short space of time that it hurts your brain trying to keep up.
Here are a few more.
Banksy (who stoked a few coals by showing the Korean animators in sweat shop-like conditions):
John Kricfalusi (creator of The Ren and Stimpy Show).