I'd create a cartoon titled "Taltar's World."
The premise for Taltar's world is that the main character, Taltar, is trying to win over this cute girl who lives in the same town. Essentially, the show goes through the daily happenings of Taltar and his friends; going to the mall, school. Also, many elements are similar to that of the Regular Show and Adventure time, but not entirely.
About halfway into the series, Taltar realizes that he does not actually exist and his world is an illusion. The first several episodes were going normally, showing elements of comedy and wacky cartoon visuals. Episode seven ends with Taltar staring into a mirror, crying. The following episodes involves Taltar interacting with his best friends, trying to gain reassurance that they are real and not illusions. Despite their attempts to convince Taltar that everything is fine, he still maintains a cold, emotionless state, contrasting greatly from his personality at the beginning of the series.
Taltar stops chasing after his crush and forgets about her entirely. On the final episode, Taltar commits suicide.