Here are some ideas for season 4. This may air in 2014.
Gumball finds a toy train that is cursed.
Gumball and Darwin find a monster in the closet.
This is a Halloween special and a spoof of Resident Evil.
Darwin destroys the robinson's house by accident and becomes evil.
Gumball must pass a big test in order to switch from public to private school
Darwin finds a strange cave, and gets lost, so Gumball must find him.
Gumball gets his sweater torn and must get a new one but apparently they were sold out of sweaters so Nicole buys Gumball a jacket instead which makes him more cooler than before.
Darwin gets bit by a vampire and tries to bite Anais, Skydancer, and Gumball.
Anais lies that Gumball was a famous person, gets a little overboard and the lieing becomes reality.
Gumball and Gummy are on a faceoff to be class president.
Anais tries to find her hidden talent.
12-The Trap: Part 1
The Whirlettes and Skydancer get traped in a tar pit, Gumball and the gang try to save them but Darling ends up drowning in the tar.
13-The Trap: Part 2
Darling is still drowning in the tar and Darwin (sort of) tries to save her from the tar pit.
The Evil Cake
Anais's birthday cake makes her evil and disloyal to her family.
Masami tries to help Gumball and Darwin to control their anger.
The Earth Day
Darwin doesn't know how everyone can make the world a better place.
Gumball and the gang meet Rosemary, a greedy, and rude dragon.
Gumball and Darwin prank Dad for a sasuage and must get him back before they get into trouble.
Gumball Becomes Lego
Gumball Destroys Banana Joe's Cousin
Darwin Destroys Penny Then He Become A New Bad Guy