From Muppet Wiki

Several Muppet projects have been conceived of having "spooky" and "scary" elements. While a majority of them have never specifically been labelled as "Halloween projects," the themes and tones of them can be characterized as "Halloween-y." For example, even though Halloween is never mentioned in episode 307 of The Muppet Show, the episode aired around October 31st in most markets. This same logic has been applied to various projects categorized here.