Smilin' Joe Fission is the official mascot of the Springfield Nuclear Power Plant and the Springfield Isotopes. He also stars in filmstrips shown to visitors at the Power Plant, like the filmstrip the plant shows Bart's class. He looks similar to The Happy Little Elves. Since the episode Replaceable You, he has rarely been seen or heard of.
- Episode – "Homer's Odyssey"
- Episode – "Homer at the Bat" (appears on baseball cap)
- Episode – "The Last Temptation of Homer"
- Episode – "Blood Feud"
- Episode – "Replaceable You"
- Video game – Bart's Nightmare
- Episode – "Homerland" (appears on Homer's convention pass)