Although Nintendo and Sega were once major rivals, they coexist pretty peacefully now... probably because Nintendo is still monolithic and Sega no longer poses a real threat. Anyway, during the '90s, it would have been basically impossible for characters from the two companies to appear in each other's games. That happens all the time today (Mario and Sonic at the Olympic Games, Super Smash Bros., etc.), but imagine what that would have looked like back then. That's what one hacker did when he put Yoshi's Island-era Yoshi into Sonic The Hedgehog 2 (via Kotaku).
The gameplay is a lot smoother than it has any right to be. Although the Sonic games are all about speed, the more leisurely-paced Yoshi exists in this world just fine. In the gameplay video above, Baby Mario is replaced on Yoshi's back by Sonic and Tails, and Yoshi carries them as he gets up to all his old tricks: swallowing stuff, making and shooting eggs, hovering.
It's a really natural-feeling experience, and the video description says it was "made by Xenowhirl for the Sonic Hacking Contest 2010." The ROM file had been unreleased until now, and while the video uploader had included a download link, it has since been removed by request. The request seems to have come from the commenter who wrote, "this hack was never [publicly] released and this is more than likely a leaked copy. Any chance you can take download links down until there's confirmation that Xenowhirl actually put this out himself? It was entered privately and to see it spreading around is very [disappointing], especially as someone involved with the contest myself."
Still, if you want to give this a try yourself, it's probably possible to find a download link. What other characters do you think would be surprisingly effective in the Sonic universe? Give us a heads-up in comments, and maybe some valiant hacker will make it happen.
Featured image: Tpot/YouTube