When a sitcom is dying, they sometimes do something ridiculous or unwanted to keep it going.

Cousin Oliver (Brady Bunch)
Jonathan Winters as Mearth (Mork & Mindy)
Jolene (Alice)
Coach moved to Florida
Laverne & Shirley moved to California
All the new kids (Cosby Show)
Seven (Married with Children)
Winning the lottery (Roseanne)
Beverly Ann (Facts of Life)
Stupid Fonzie storylines (Happy Days)

Thank goodness they didn't rescue the castaways on Gilligan's Island!

Also:

Lily on Step By Step

After Ron Howard (Richie) left the series, Ted McGinley joined the cast as Roger Phillips the new Phys Ed teacher at Jefferson High and nephew to Howard and Marion.

Billy Warlock joined the cast in season 10 as Roger's brother Flip, along with Crystal Bernard as Howard and Marion's niece K.C.

Adam on Bewitched

Annie on Family

Andrew on Family Ties

Sam on Diff'rent Strokes

Ricky on Partridge Family

I completely agree about Roseanne. The final season was PITIFUL.

Good call on the later Fonzie stories as well. He became a parody of himself.

-Billy on Who's the boss?
-Olivia on The Cosby Show she was useless to me the most anoying kid in sitcom history

-Billy on Who's the boss?
-Olivia on The Cosby Show she was useless to me the most anoying kid in sitcom history
I remember Billy. BAAAAAAD move. At least they realized the mistake and wrote him out the next season. YAY!!

When a sitcom is dying, they sometimes do something ridiculous or unwanted to keep it going.

Cousin Oliver (Brady Bunch)
Jonathan Winters as Mearth (Mork & Mindy)
Jolene (Alice)
Coach moved to Florida
Laverne & Shirley moved to California
All the new kids (Cosby Show)
Seven (Married with Children)
Winning the lottery (Roseanne)
Beverly Ann (Facts of Life)
Stupid Fonzie storylines (Happy Days)

Thank goodness they didn't rescue the castaways on Gilligan's Island!they did rescue the GI castaways; in the first of those HORRIBLE GI TV movies in the 70s.

I remember Billy. BAAAAAAD move. At least they realized the mistake and wrote him out the next season. YAY!!
It was a bad move. Sam and Johnathan were pretty much too old for heart to heart chats with Tony so I guess they tried to bring that back by adding billy.

On A Different World:

Freddie changing her hairstyle and her "ways" and becoming more conservative.

Freddie and Ron hooking up.

LH went on for one final season with a new title (A New Beginning) and many regulars gone. Melissa Gilbert and Dean Butler were now the headliners, but the magic was gone and after 3 additional TV movies, the show came to an end.

The Waltons added Peggy Rea (later of Dukes of Hazzard and Step by Step) as a cousin or aunt of the Walton family after Michael Learned left the show. She also had her grandkids, which never bodes well for a sinking series. There were quite a few Walton reunion movies made (the last about 10 years ago), but the show was without its mother figure and never recovered. :(

MORK & MINDY getting married, Tony Nelson & Jeannie getting married

Whenever a kid aged rapidly between seasons

when Leonardo DiCaprio was added on to play luke on growing pains