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Tearjerker: Invader ZIM
The Sad, Sad Tale of Chickenfoot, where Chickenfoot talks about his past life with dib where he was a normal man named Chewie Rodriguez until an accident occurred when the microwave was splashed with water while Chewie was wearing the suit and cooking chicken in a microwave, generating an explosion that "created an unholy fusion of man and chicken", causing him go insane and live all alone in an apartment with assorted Chicky Licky toys that he calls his "friends".
Bad, Bad, Rubber Piggy doubles as both horror and Tear Jerker worthy because of what Zim does to poor Dib by crippling him horribly by tossing rubber pigs into Dib's past through a time machine, replacing seemingly random objects in ways that cause Dib to have horrible accidents, progressively crippling Dib to the point that he almost dies.
Bloatey's Pizza Hog, Gaz yells at Dib for going off to fight Zim because she "just wants to go out to eat with dad." Considering the situation, this certainly counts.
Bloaty. The poor man is completely miserable, and its possible we see him pass away at the end.
Although his situation is no less tearjerky, Rikki Simons confirms that Bloaty is alive.
How could one forget the MASSIVE tearjerker in which we see an adorable experiment in an isolated room of a spaceship, who hopes someone will rescue him... only to have ZIM nonchalantly leave? The poor creature is left to cry softly...
The ending of Dib's Wonderful Life of Doom. Poor Dib. Just when things were starting to look better...
"OH, GIR! GIIIIR! THEY'VE TURNED YOU INTO GROUND BEEF! HOW? WHY?????"
Dib and Gaz's.......situation. Their dad is so busy, they only go out to eat together ONCE A YEAR. Which seems sort of funny... until you think about it......