Despite being lauded by fans and critics alike during the first three seasons, for some reason, Community just wasn't producing a high viewership. Unfortunately, that played something of a part in the series creator, Dan Harmon, being let go prior to season four. That's where some of the trouble began.
It's generally accepted among the public that season four is where Community started to slide off the rails (mainly because of Harmon's exit) and the quality of the season certainly reflected it. Future seasons would even call it the "gas leak" year. Season four produced a top-score on IMDb that wouldn't have even cracked the top-ten in any of its three previous years.
History 101, Episode 1 (7.3)
Right off the bat, the premiere episode of the season felt just a tad off when Abed pictured his (and the gang's life) as a three-camera sitcom when the group returns from summer, calling it his "happy place." Meanwhile, Jeff reveals to the group that he's only one history credit away from graduating, causing them to freak out on him for wanting to graduate early.
However, the Dean doesn't want Jeff to leave either and concocts a plan to keep Jeff out of the lone history class of the semester, which ultimately ends up working, forcing the Dean to apologize and then offer another history class so that Jeff can graduate.
Conventions of Space and Time, Episode 3 (7.3)
One of the show's many recurring staples was the show "Inspector Spacetime," a spoof on Doctor Who, and Troy and Abed finally decided it was time to go to an Inspector Spacetime convention.
However, at the convention, Abed starts bonding with Toby, a fellow Inspector Spacetime fan. Troy becomes jealous and the two wind up in a mini-fight. Then, when Troy realizes that Toby is trying to steal Abed away from him, he comes to his best friend's aid and the two make-up.
Paranormal Parentage, Episode 2 (7.5)
While the prior three Halloween episodes had taken place in the study room, the show switched things up this season when the gang made their way to Pierce's mansion. Pierce, having accidentally locked himself inside his safe room, tells the group that he thought he saw the "ghost of his father."
This then sets off a series of spooky-hijinks where everyone gets separated as they try to find their way around the haunted mansion... only for it to be revealed that the "ghost" was Pierce's half-brother, Gilbert.
Cooperative Escapism in Familial Relations, Episode 5 (7.5)
Talk about family issues. During this Thanksgiving special, audiences were introduced to Jeff's dad when Jeff finally managed to call him and schedule a meeting. However, Jeff discovers that he has a younger half-brother, whom his father had to raise by himself when his second wife passed away, and Jeff finally accepts that he doesn't need to have his father in his life (especially since his father was a jerk).
Meanwhile, the rest of he group gets trapped at Thanksgiving dinner with Shirley's entire family, eventually hiding out in the garage in order to avoid all of the drama.
Advanced Documentary Filmmaking, Episode 6 (7.5)
After the Chang Dynasty ended at the conclusion of season three, Chang still somehow managed to make his way back into Greendale - only this time, it was as Kevin. He shows up with amnesia and Abed decides to shoot a documentary following the school's attempts to heal him. Shot in "mockumentary" style, Jeff is the only person at Greendale who doesn't buy Kevin's act and tries relentlessly to get Chang to fess up and admit it.
In the end, Jeff finally gives up and accepts that Kevin is real... only for Chang to secretly pull out a cellphone, call an anonymous number, and inform them that their plan is working.
Intro to Knots, Episode 10 (7.6)
Most holidays are supposed to be happy, joyous occasions... this particular one turned into a kidnapping. The Christmas special for season four had the study-group throwing a party for their history professor in order to try and bump up the failing grade they received on the last paper. Then, through a series of unfortunate events, Professor Cornwallis ends up tied to a chair in the apartment (mostly thanks to Kevin) resulting in the group holding him hostage for a better grade.
However, it's then revealed that Cornwallis was never tied up (again, thanks to Kevin) and that he played along with the charade because he was feeling lonely during the holidays.
Advanced Introduction to Finality, Episode 13 (7.7)
The season four finale played heavily on the "darkest timeline" staple, allowing all of the gang's evil-counterparts to enter their timeline and try to take it over, all with the ultimate goal of getting Jeff to take a job at his old law-firm upon graduation. In a high-tech, advanced final battle, the show manages to bring back another staple (paintball) as the study group faces off against the evil-study group.
Of course, in the end, the entire episode is revealed to have been playing out in Jeff's head (before he rolled a die), resulting in him choosing not to roll it at all. They move on to Jeff's graduation ceremony, and Jeff finally moves on from Greendale (but not for long).
Herstory of Dance, Episode 8 (7.9)
Britta's stubbornness hardly ever paid-off, but this was one of the few episodes where she was able to savor a victory. After misspeaking in the study room and informing everyone that she wants to throw a "Sophie B. Hawkins" dance (instead of a Sadie Hawkins dance) Britta decides to make it happen by actually getting Sophie B. Hawkins to show up.
Expecting Britta's attempts to fail, Greendale still throws a normal Sadie Hawkins dance at the same time... only for Sophie B. Hawkins to actually show up at the last minute and stun everybody, including Britta.
Basic Human Anatomy, Episode 11 (8.0)
It was no secret that Troy and Abed were the best friends of the entire series, but even they got thrown for a loop during this episode when the two ended up "switching bodies" the day of Troy's one-year anniversary with Britta. Abed (pretending to be Troy) then goes on a date with Britta, while Troy (pretending to be Abed) goes with Jeff to try and find a way to make the two friends return to their own bodies.
By the end of the episode, it's revealed that Troy and Abed are doing this "bit" because Troy wants to break up with Britta, but doesn't know how to without hurting their friendship in the process. Troy and Abed finally switch back, Troy and Britta break-up but stay friends, and everything goes back to normal.
Heroic Origins, Episode 12 (8.2)
Just try to ignore the plot holes. Although ripe with inaccuracies, the top-rated episode of the season was still the most entertaining as Abed spends the entire time trying to determine the group's "origin story" and how they all managed to make it to Greendale.
However, in his research, Abed uncovers clues that lead to the revelation that the entire group had ties to one another in the past... oddly enough, all of those ties were ultimately what led everyone to attend Greendale in the first place, making the implication that the Greendale Seven were always meant to find each other.