This is an idea for season 8. It contains 4 episodes.
Gumball thinks that Darwin is an alien.
Gumball finds a skunk which causes him to smell.
Gumball admits to Penny, that he is in love with her.
Gumball gets to graduate on the last day of school, but Darwin didn't graduate, causing Gumball to go to College without him. In the end, Gumball leaves and writes a note to Darwin, saying: "see you soon!". And everybody said bye to Gumball.