"Sheen's Brain" is the 30th episode of The Adventures of Jimmy Neutron: Boy Genius.


After Sheen fails a history test, Jimmy uses his reconfigured Brain Drain Helmet to increase Sheen's brain to be larger and smarter so he'll pass his math test. He passes but soon becomes evil with his new mental powers and plots to destroy all of Retroville and rule the world. Now Jimmy and Carl have to stop him from plunging Retroville into mass destruction and chaos and get him back to normal or else his brain will cause his head to keep growing until it explodes.


  • This episode was ranked #72 in The 100 Greatest Nicktoon Episodes countdown.
  • Sheen firmly believes in Ultra Lord, even when he's a god.
  • Sheen wrote the Ultra Lord website.
  • Since only Sheen's brain was supposed to grow and not his head, it should've already exploded.
  • This is the first time one of the Jimmy Neutron protagonists becomes evil; it would happen again, ironically with Libby, in "The Tomorrow Boys", since Sheen wanted to make Libby his queen.
  • Sheen killing his friends and then tearfully regretting it could be a reference to the story, "A King and his Hawk" in which the king regrets murdering his dear friend.
  • Sheen's answers were:
    • Ultra Lord is the father of the whole planet.
    • When Ultra Lord beat Megalon playing chess, his score was four...
    • On Planet Xaradan where Ultra Lord goes on vacation.
    • A dragon thought it was a hat and it was too small.
  • Footage from Ultra Sheen appears in this episode.
  • This is third time a character changes and then goes back to normal. The first was in Normal Boy and the second was in Make Room for Daddy-O.

Home video releases

  • The Adventures of Jimmy Neutron: The Best of Season 2

"Gee, this is harder than I thought."
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