5. Adventure Time helped alleviate the stigma of mental illness
Perhaps the cartoon's single best message comes from Princess Bubblegum in Season 7 Episode 1 "Neddy". While dealing with the erratic behavior of her brother Neddy, she tells Finn and Jake: "People get built different. We don't need to figure it out, we just need to respect it."
Some people read Neddy as suffering from anxiety, others see him as a trauma victim, but either way Adventure Time has a rich cast of characters who either experience mental illness or are not neurotypical. Many viewers consider, and while his lack of empathy and social awkwardness accounts for much of his humour, Princess Bubblegum is quick to dismiss any attempt to "fix" him, instead preferring to help create a situation where Lemongrab can be happy.
We also see the Ice King evolve from a crazy, one-dimensional foe who kidnaps princesses into a complex and fully-fledged character who lost his mind and is still worthy of patience and empathy. The message of respecting each other, especially those who are ill or struggle socially, is of mammoth importance to young viewers watching in-between stints in a classroom or playground setting.
With a heavy heart, myself and thousands of other fans this week bid farewell to a most beloved cartoon. The way Adventure Time conjured silliness and sophistication (often in the same frame) is to be lauded, and its delivery of profoundly important messages to viewers is unparalleled.