The American arcade game world record holder has been awarded $350,000 in damages after emerging victorious in a defamation lawsuit against a YouTuber.
Mr Mitchell, 59, first rose to fame in the 1980s during the arcade game golden age, breaking Donkey Kong records and becoming the first person to claim a Pac-Man perfect score.
Dubbed the "King of Kong", he claimed another win on Tuesday when Brisbane District Court Judge Ken Barlow handed down his judgment following a trial in September and October.
Queensland-based Karl Jobst posted a YouTube video online for 15 days in 2021, claiming Mr Mitchell's prior lawsuit against another online creator left the young man "deeply in debt".
The American claimed the video implied his actions had contributed to YouTuber Benjamin Smith, who went by the screen name "Apollo Legend", taking his own life.
Judge Barlow found Mr Jobst had taken part in a vindictive crusade against Mr Mitchell with a "reckless disregard for the truth".
"Clearly he wanted to be the knight who slayed the Mitchell dragon," he said.
"His lance was not as strong as he thought it to be."
Mr Mitchell was not in court on Tuesday for the judgment, but he posted on X there was "nothing like the smell of victory".
About 5000 people watched via YouTube live video as the decision was handed down.
Mr Jobst also made videos about people who accused Mr Mitchell of cheating in obtaining his high scores and the American's subsequent lawsuits against them.
Judge Barlow said it was not his role to determine the truth of the cheating claims.
"(Mr Jobst) seems to see himself as a crusader against Mr Mitchell - one of the last people sued by Mr Mitchell and the only one who has not backed down," he said.
The judge referred to an interview in which Mr Jobst said: "Billy Mitchell needs to be destroyed in court … I am the last chance for the public to punish Billy."
Mr Jobst was present for the judgment.
Asked outside court how he was going to pay the damages, Mr Jobst said "with money".
He later posted on X he would consider his options and work hard to repay supporters "all that you are owed".
Judge Barlow found Mr Jobst's video had "caused substantial additional damage to Mr Mitchell's reputation and caused him distress".
"He was reckless in making the allegations," the judge said.
"His assertions were based on a fallacy, that Apollo Legend had paid a large sum of money to Mr Mitchell."
Mr Mitchell filed his defamation lawsuit in September 2021 against Mr Jobst, who is known for making videos about video game records and cheating scandals.
The Florida resident claimed his reputation was damaged and he lost out on substantial paid work at gaming conventions as a result of a video Mr Jobst posted in May 26 that year.
Mr Mitchell previously gave evidence that he was physically sick when viewing the video, which he said implied he "hounded a young man to commit suicide" by suing Mr Smith.
Mr Jobst's original video was seen by more than 500,000 people, the court heard.
Judge Barlow said Mr Jobst was vindictive towards Mr Mitchell by uploading the video multiple times and failing to apologise to him directly.
Mr Jobst was also criticised for issuing a retraction at the end of a 30-minute YouTube video containing unrelated gaming content.
The American was awarded $300,000 in non-economic damages and $50,000 in aggravated damages.
Judge Barlow said Jobst should pay $34,668 in interest dating back to the first publication of his video and pay Mr Mitchell's costs, subject to submissions from each side.
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