It's pretty crazy. Jhonen Vasquez's most notable work previously was literally a comic about a guy who kidnapped people to murder in his basement, so it's not like they didn't know what they were in for.

Invader Zim has an episode where he is concerned that a school health inspection will out him as an alien so he begins systematically hunting down the other children and harvesting their organs to stuff inside his own body until he's a bloated monstrosity.

Nickelodeon Execs: "This is fine."

The funny thing is that it might have been on the air even longer if the show wasn't costing so much money. They were recording voice lines for some characters while the actor was suspended from a sort of crane-mechanism. Weird stuff all around.