Crud, i don't want to ruin the last 0.0000000000000000000000001% left of my childhood, what's it about?
EDIT: Okay, nevermind, I watched it, not really that depressing except for Mr. Krabs and the ending. ;(
I guess it wasn't THAT depressing, but it's still kinda... Childhood ruining.
Speaking of ruining your childhood, has anyone read the Rugrats Theory? As far as Creepypastas go, it's one of the best cartoon pastas.
Have you heard of lavender town syndrome? It supposedly had occasional high note that could be heard with headphones. The story is that kids who listened to the lavender town music (original) got splitting headaches and started coughing up blood. Thoughout a few more symptoms, It eventually led to the kids committing suicide.
Try reading the Holder Series creepypastas. They gave me rather depressing moods in my gut. Especially the:
a. Holder of Youth
b. Holder of Innocence
c. Holder of Peace
d. Holder of Love
e. Holder of the End