Aborted Arc: Bernie and Andell's secret relationship in the third season eventually culminates in the two getting engaged despite everyone's flippant reaction to the two lasting together. By the 5th season, the two are not seen interacting much. When Andell migrates to The Parkers, the engagement plotline is simply dropped.
Frank and Dee trying to have a baby of their own also dropped after carrying through a couple of seasons.
Aerith and Bob: Frank (normal name), Dee (usually a nickname), Myles (normal name spelled differently), and Moesha (very unique name).
Ascended Extra: Niecy evolved from a friend at the Den with almost no lines in the pilot to one of the core cast members and Moesha's best friend by the final season.
Beware the Nice Ones: When Alicia spread a rumor about Moesha sleeping around with several men, including Alicia's boyfriend in "Gimme A Break", Moesha confronted the other girl in her usual diplomatic and demands an apology. When Alicia refused and proceeded to call Moesha "Hoesha", Moesha immediately lunged for the girl, only to be held back by Niecy, who had to restrain Moesha twice. As Niecy dragged Moesha out of the cafe, Moesha made it known that she would come back to finish the job.
Moesha and Miss Moss at least until the Alzheimer's kicks in
Invisible Parents: For a show with such a strong focus on Mo and her family, the fact that none of her friends' parents ever appear really sticks out. Averted with Kim when Nikki Parker finally makes her debut to set up The Parkers.
Karma Houdini: Frank, in one episode. For the sake of peace in the family, he asks a reluctant Moesha to accede to Dee's signing her up for modeling classes behind her back. When the situation blows up (Dee is impossible to deal with), Frank then plays peacemaker - looking good over calming down a situation he caused. Or, Frank - you could have stood up to your wife in the first place.
Myles gets caught smoking weed and Frank signs him up for therapy that eventually extends to the whole family. This is the same Frank that banned Moesha from dating, forced her to go to another school, compared her to a tramp, drove her out of her own home for an entire summer, tried to get her to take a drug test, and forced Dorian into boot camp. Myles gets to play video games with his therapist.
Re Tool: Started with the 5th season. The many changes during the college years include the Genre Shift from Sitcom to Dramedy, the departure of two major characters, sudden abortion of multiple story arcs, intense focus on a new character over others, sudden revelations about characters' backstories, a new soundtrack, as well as the abandonment of several of the show's quirks including Moesha's opening and closing narrations for every episode and the unique visual moments between scenes.
Wicked Stepmother: Dee averts this. Though it is implied Moesha's mother, Marguerite, was this to Dorian, threatening to divorce Frank if he did not abandon him.
Hell, his birth mother isn't much better...
Writers Cannot Do Math: It is implied that Moesha does not remember her mother, despite the fact that she would have needed to have survived long enough to have Miles.
This is also a case of Depending on the Writer. In an episode where Moesha accuses Dee of trying to get rid of her mother's furniture, she has several vivid flashbacks of her childhood with her mom and the couch Dee tried to sell. In the last season when Frank explains how his relationship with Barbara Lee started, Moesha draws a complete blank on the time period her parents were separated even though it wouldn't have been too far removed from the previously mentioned flashbacks.
You Look Familiar: Ray J appeared as Charles in seasons 2 and 3, himself in season 4, and Dorian in seasons 5 and 6.