In 1999, an ambitious crossover game allowed players to experience the video game fights of their dreams. Who would win in an actual fight between Mario and Donkey Kong? Could Samus overtake her fellow space traveler Fox McCloud? What if in his travels, Link encounters Pikachu? These questions may or may not have entered your consciousness before Super Smash Bros. launched on Nintendo 64, but the idea of video game characters leaving their respective games to meet on a battlefield ignited players’ imaginations. Soon, players were fantasizing about what other characters could make their way into a sequel.
Source: Game Informer Super Smash Bros. Ultimate Is A Crossover Event 20 Years In The Making