Took a Level in Dumbass

smiler to Badass decay but with the Characters' intelligence. Basically it's when a Character gets stupider.

The character above is Captain Hook, a much-loved villain of Peter Pan. He came back to menace the kid heroes of the Dora-esque show Jake And The Neverland Pirates, missing about half his brain cells and with a somewhat off-putting redesign. Granted, Hook has always had trouble defeating children, but in this case it is particularly glaring.

Other Examples
Maka Albarn from Soul Eater( She went from badass bookworm to impulsive hot blood.)
Sailor Venus from Sailor Moon.
Gourry from Slayers .
The Team Rocket trio from Pokémon.
Alphonse in the 2003 anime version of Fullmetal Alchemist.
Homer Simpson from The Simpsons.
SpongeBob from Sponge Bob Square Pants.
In The Fairly Oddparents: Pretty much every character with the exception of Wanda(especially Timmy and Cosmo.)
All of Hank Hill's friends from King Of The Hill.
Chowder from well Chowder.
Daffy Duck from The Looney Tunes.
Jake from Adventure Time.
T.J. from Recess.
Ben sometimes from Ben 10.
Dr Robotnik from Sonic Sat Am.
Batman in Dark Knight Rises.
Beast Boy in Teen titans