While Mario and Sonic and their respective casts face off every few years in their Olympic Games crossover games, Sonic creator Yuji Naka still has not given up on his original idea. He gave an interview with Famitsu recently where he discusses what he originally envisioned for a crossover
Actually, I wanted Mario [and Sonic] to appear together, so one time I went to give Miyamoto-san a presentation on how I want to create an action game which is co-starred by Mario and Sonic. It was in the GameCube days, and I took around four planners with me. It is a pity that the discussion was ‘clearly it isn’t necessary for Mario and Sonic to co-star in an action [game]’ and it didn’t become a reality, but SEGA was able to get the license for the Olympics just at that time, so in order to make the best use of the license, companion characters appeared together. A little later Sonic appeared in Super Smash Bros. Brawl. However, this too came into reality because I requested from Sakurai-san, ‘I want Sonic to appear [in Smash Bros.]’. The Olympics is a bit different from my wish, but I think it’s a good thing that children around the world are happy about them co-starring. But someday I want to realize an action [game] together with Mario. I think I’m going to give another presentation so that Takashi [Iizuka] finds the necessity [of a Mario & Sonic action game] (laughs).
Original Sonic designer Naoto Ohshima, who participated in the interview as well, also chimed in with the following:
“I also agree. Previously they were considered rivals, but when I saw them co-starring, I honestly thought that Nintendo acknowledged Sonic.”
I and no doubt millions of others, would love to see a true crossover between Sonic and Mario. I hope that one day, Yuji Naka is able to help get this game made.