Aaron Gage noticed how the lyrics to “Deck the Halls” would fit into Black Sabbath’s “War Pigs.” Viewers at reddit clamored for the whole song, but he said he didn’t want to wear out the welcome, and the rest of the song didn’t fit quite a well as this part. I have to say that I agree- once you’ve heard the joke, there’s no reason to drag it out to feature-length. But it’s a good joke.
Source: neatorama