Metroid Prime had the Fusion suit already on the disc, but you couldn't unlock it unless you connected your Gamecube to a Gameboy Advance while the game Metroid: Fusion was playing in it. This was Nintendo encouraging you to buy an entirely new game to access the Fusion Suit. Not all of the games I mentioned had new worlds to unlock on disc via DLC, but they all had varying levels of content on them that you had to do something outside of owning the game to unlock them. Go look it up