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The recent Switch Online + Expansion Pack release F-Zero Climax is celebrating its 20th anniversary tomorrow. As part of this, former Nintendo employee Takaya Imamura (who worked on the GBA title and the F-Zero series) back in the day has shared a special code.
This code which commemorates the anniversary can be input in F-Zero Climax and unlocks a special course. Here's a rough translation:
"The recently released [F-ZERO CLIMAX] will celebrate its 20th anniversary on October 21st! To commemorate this, we have created a course, so we will be releasing the password! (Please enter in order from image 1)"
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To input this code, you'll need to boot up the Switch Online Game Boy Advance app and F-Zero Climax, and from 'mode select' navigate to edit > edit > password and input the above code. Be warned, it might take a while!
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Apart from F-Zero Climax, Nintendo also recently added F-Zero: GP Legend to the GBA's Switch Online service.