Flukes are a unique (and can be, at times, clever) form of fan art, which rely on comedy, but the jokes are very rarely pulled off successfully. Stripped down to the most basic definition, flukes are small pictures (as if screenshotted fresh off an emulator) made to look like scenes from EarthBound. That's precisely what we're looking for, and not one-panel sprite comics.
For further information, refer to the topbar for official Guidelines and the FAQ. At the topbar, you can also find downloadables to help you with the flukemaking process.
