Moon Fiends are the idiotic and evil blue aliens that live on the moon who made their first and only appearance so far in Johnny Gets Mooned.
A bunch of evil Moon Fiends attacked Johnny and Dukey in outer space when they came to the moon to do research for Johnny's paper. The army of Moon Fiends ate a lot of spice cheese nachos, which gave them stink gas and fart on Johnny and Dukey. The leader sent all moon fiends, and later mega fiends, to attack the duo, only for Johnny to use the knowledge from his report (and the report itself) to defeat them all and escape. A Moon Fiend can also be seen in the intro of Season 1.
The Moon Fiends wear white pants and shirts, blue gloves, they have light blue skin, their heads resemble rear ends, they have green stench coming out of them, and they have creepy voices when they speak. As a result of their appearance, Johnny calls them buttheads.