"The Ultimate Showdown" is a massive, citywide battle set in Tokyo started by Godzilla and Batman, ultimately lasting for a century and involving dozens of pop-culture icons, real and fictional, ending with Mister Rogers emerging victorious and then committing seppuku. It gained a large cult following among web enthusiasts^[2] and became the "User's Choice" on December 22, 2005, on Newgrounds, where it has been viewed over 13.2 million times.^[3] It appeared on several other websites including Albino Blacksheep,^[4] YouTube, Flashportal, Transbuddha, and Weebl's Stuff. In 2006 it was included on Lemon Demon's fifth album Dinosaurchestra.^[5] It had over 25 million views on YouTube as of November 2020.^[6] A higher resolution fan upload has received over 7.5 million views on YouTube as of March 2024.^[7]

The song topped the "Funny Five" on The Dr. Demento Show for several weeks and was the #1 Request for 2006. The video has since been parodied and referenced repeatedly in other flash videos. A new version of the song was later recorded specifically for the Rock Band Network and was released for the service on July 6, 2010, under the title The Ultimate Showdown (RBN Mix). In 2009, the song was rerecorded with a full band, and this track was included in Lemon Demon's 2011 EP "Live (Only Not)".^[8]

In early January 2021, the first copy of the video to be uploaded on YouTube was taken down by Shawn Vulliez, the original animator. He reuploaded the video to his own channel 'Srsly Wrong'.^{[9][non-primary source needed]}

For the 15th anniversary of the original animation's posting, Blabberdookie and Warddraws hosted a collaboration of animators to create a new version of the original video. It was released on 22 October 2021.^{[citation needed]}

As Godzilla is going on a rampage through Tokyo, Batman surprise-attacks him with a Bat-Grenade. Godzilla's attempt to retaliate is blocked by Shaquille O'Neal, who is attacked by Aaron Carter until Batman runs over them both with the Batmobile. Before Batman can return to the Batcave, Abraham Lincoln rises from the dead and shoots Batman with an AK-47. Lincoln is then forced to flee by Optimus Prime.

After Godzilla eats a piece of Optimus Prime, Shaq returns but is then attacked by Jackie Chan. Meanwhile, Lincoln attempts to finish off Batman with a machete, but is stopped by Indiana Jones. Jones is left defenseless against Godzilla as Batman steals his gun and unsuccessfully attempts to kill Chan. A somersaulting Chan and a pole-vaulting Lincoln collide in midair and are killed by a Care Bear stare.

Chuck Norris, presented as a godlike figure, descends from the sky to angelic tones, kicks Indiana Jones in the groin, and decapitates Batman (who has changed back into Bruce Wayne) with his thighs. Then Gandalf the Gray, Gandalf the White, Monty Python and the Holy Grail's Black Knight, Benito Mussolini, the Blue Meanie, Cowboy Curtis, Jambi the Genie, Robocop, the Terminator, Captain Kirk, Darth Vader, Lo Pan, Superman, every single Power Ranger, Bill S. Preston, Theodore Logan, Spock, The Rock, Doc Ock, and Hulk Hogan all arrive and kill Norris.

Approximately a century later, the battle has officially ended and is implied to have claimed the lives of many more characters besides those mentioned, with only one contestant remaining: Mister Rogers, who commits seppuku.

• Lemon Demon official website
• "The Ultimate Showdown" on Newgrounds