Courage the cowardly dog is my favorite cartoon show and character of all the time. Despite the show's reputation of it being comedy/horror, I can remember sad episodes and moments.
Observe the relationship between Eustace and his mother, both of them cruel, cold people. Eustace is the way he is due to his mother, and, if one episode in particular is anything to go by, his mother was made this way by a loved one too. Two of the biggest rule and impolite people in the show are the result of a cycle of abuse.
Remembrance of Courage Past episode: which shows how Courage met Muriel. Especially with the revelation that his parents were put on a rocket and shot into space by a sadistic vet, with Courage outside the rocket trying to stop it. He escapes the vet by going down a trash chute and you see him land in a dumpster, and he waves to the rocket flying away. Muriel finds courage with panties crying near the garbage and she adopts him.
The Curse of Shirley, where a hallucinating Eustace takes pity on a young version of himself. Eustace, by all means the biggest selfish jerk ever portrayed on any Cartoon Network show. Eustace: "No hat? That's not right, little boy without a... a little boy should have a hat." It's even more sad if you consider that Eustace was seeing this through a mirror that was meant to show one's true self. It was broken beforehand, but it may have been showing that Eustace is, deep down inside, a sad man who lashes out at everyone due to a painful childhood.
The Queen Of the Black Puddle, a ghastly woman charms Eustace and takes him to her world, and no surprisingly, Courage doesn't give a damn, and he has all the right not to. But he then sees how Muriel is devastated by having her husband taken from her, crying her heart out, and Courage realizes he'd rather put up with Eustace's crap for the rest of his life than to see his benevolent owner suffer. The episode makes it very clear (or sad) to see that Courage saves Eustace, even though he doesn't deserve it, because his love for Muriel spoke louder than his dislike of Eustace.
The Hunchback of Nowhere, A lonely and deformed hunchback goes from door to door just seeking shelter only to be called ugly or a freak by everyone, including Eustace, and having them slam the door in his face. He and Courage build a friendship that's both heartwarming and as Courage shows the poor soul kindness for once in his life. And the climax only adds to this: as Courage and the Hunchback put on a show for Muriel, Eustace tries to ruin it. The Hunchback's response? He puts on a Eustace mask and forces him to see himself for who he is, which is only more heartrending when you realize that it's not just Eustace: it's for all the people who have said he's just a freak.
As so on...
I am not really sure why is it considered a comedy/horror show, it is a drama cartoon with a many adult topics. Is it truly sad or not?