Shows that had yearly special episodes specific to them?

[TMC]

In other words, episodes with certain theme you always look forward to that’s unique to a particular show.

For example:

• Community's paintball episodes.
  
• Brooklyn 99's heist episodes.
  
• The Drew Carey Show's live shows, as well as the April Fool's Day episodes where the audience must find "intentional bloopers".
  
• The "Treehouse of Horror" episodes on The Simpsons.
  
• The "Bar Wars" episodes of Cheers, first starting in Season 4 and skipping Season 5, then appearing yearly thereafter with two episodes in Season 10.
  
• Degrassi had a few years running where they adopted a telenovela format for the summer and aired new episodes Monday-Thursday for about two months.
  
• MASH had the "Dear Dad" episodes, where they were from the point of view of Hawkeye writing to his dad telling him about what's going on in the camp. This morphed into other episodes with other characters writing letters such as "Dear Mildred", "Dear Sigmund", etc.
  
• ER had its Africa episodes, where one or two characters would go to an African country to volunteer.
  
• The Doctor Who Christmas and New Year's specials.
  
• Friends would always do a Thanksgiving episode, usually featuring a special guest (Brad Pitt, Christina Applegate, etc.).
  
• Family Guy's "Road To" episodes.
  
• Bob's Burgers Thanksgiving episodes.
  
• Roseanne's Halloween episodes.

If you want to count recurring characters that showed up at least once a season, there's Lilith's appearances on Frasier, the annual Sideshow Bob episodes on The Simpsons, or Q on Star Trek: The Next Generation.

While they didn't do it every season, most seasons of Night Court would have an episode where they would have to spend an entire evening to clear out a huge backlog of cases. And there always was some kind of stipulation involved like trying to break a record or to clear the docket before the statue of limitations expired and any case that wasn't tried would be thrown out.

[merlinjones]

Mary Tyler Moore's failed parties and Teddy Awards episodes (not necessarily annual).
Bewitched Halloween episodes (not necessarily annual).

[TMC]

The Goldbergs parodying/making heavy homages to one particular movie from the '80s (for example, Airplane or Bill & Ted's Excellent Adventure as the more recent ones) for their season premieres.