A list of T.V. shows that declined in quality after a certain event happened. These shows can be ongoing, just have lost quality after a certain moment on the show.
1 Happy Days - Fonzie jumps a Shark (literally)
The obvious first, as this show did it literally AND figuratively!
2 Roseanne - Roseanne and family win the Lottery
3 Heroes - Peter gains Amnesia
4 The X Files - Mulder leaves
5 Dallas - It was all a Dream
6 Brady Bunch - Cousin Oliver joins the Family
7 Doctor Who - The Doctor restarts the Universe
8 Smallville - Clark reverses time to save Lana
9 Family Guy - Brian dies
10 Fairly Odd Parents - Poof is Born/Timmy Adopts Sparky
These two go hand in hand together.
Plus: the introduction of Chloe
11 Spongebob Squarepants - Spongebob feeding Gary to Puffy Fluffy/Mr. Krabs scaring Plankton into committing suicide
Its almost as if they were purposely trying to get the show cancelled. - egnomac
Two of the most dark and wicked (as in bad…) moments in SpongeBob history!
12 Regular Show - Margaret returns to the main cast
13 Magical Girl Lyrical Nanoha - Vivio becomes the main protagonist
14 Lost - The Smoke Monster
15 Family Guy - Peter trying to marry Chris
16 Family Guy - Screams of Silence: The Story of Brenda Q
17 Spongebob Squarepants - Spongebob getting a splinter
18 American Idol - Nicki Minaj appearing as a judge on the show
She doesn't even have any talent.
19 Family Guy - Brian giving Stewie herpes
20 Family Guy - Seahorse Seashell Party
21 The Flintstones - The Great Gazoo
22 The Brady Bunch - Cousin Oliver
23 Rugrats - Dil is Born/Chaz Married Kira
24 Pokemon - Misty leaves
25 Monday Night Raw - The Death of Mr. McMahon
26 Arrow - The "Death" of Oliver Queen
27 Rugrats - The Addition of Dil and Kimi
28 The Middle - Brick's voice cracks
Season 4 of The Middle - anonygirl
29 Reba - Cheyenne becomes pregnant with her second baby
30 Roseanne - Dan dies