Sonic was one of my favorite series as a kid. As much as I loved Mario, I would consistently play Sonic 1 and 2 more often (though Donkey Kong Country was probably my most played platformer). It blew my mind when I figured out that you could play as Knuckles in 2 by sticking that cartridge into the Sonic and Knuckles cartridge. I remember sitting down one day and trying to stick all of my Genesis cartridges into that one just to see if something cool would happen in those as well. Unfortunately, I couldn't play as Knuckles in my Thomas the Tank Engine game I had or in Quackshot starring Donald Duck.