Jonny Quest/Nightmare Fuel


 * The Invisible Monster. Created from a lab accident, you can only see it by the footprints it leaves. Everything it touches either dies or violently explodes. On top of that, it makes a creepy high-pitched wailing sound. Combine that with ominous music every time it's around, and you have the scariest episode in the series.
 * Plus The Movie Jonny quest vs the cyber insects. The bugs are kinda creepy, but not really on the level of nightmare fuel; but then Dr. Zin kills all of his human assistants! Thankfully, two of them are off-screen -then the last one is turned into a human popsicle and crashes to the floor into several pieces.