Nintendo’s trailblazing Game Boy marks its 25th anniversary Monday with the portable device’s legacy living on in cutting-edge smartphone games and among legions of nostalgic fans. The Japanese firm released its 8-bit Game Boy on April 21, 1989. Billed as a “handy game machine”, few knew it would turn the console-based industry on its head, starting a revolution that did for portable gaming what Sony’s Walkman had done for mobile music.