Wait... Majora, the spawn of both of them?

o.o


But uh, this is a very good question. Considering that they seemed to take special precaution in designing Malladus in a way that, at the time of ST's release (2009), alluded back to Ganon (beastly, two horns, red flowing hair/beard), who now after Skyward Sword alludes back to Demise, I think we can say they are connected.

But then Malladus was involved on some big war with the light spirits and sealed on a land totally different from the one Demise/Ganon frolic upon. So, I dunno.

Maybe sometime after SS he broke free from... whatever, and flew off to New Hyrule, and did his business, got sealed, and, uh... reincarnated as Ganondorf while his demon form was sealed in New Hyrule?

Yeah, as much as I'd like it to, Demise = Malladus doesn't really work. But I'd be willing to bet that the developers want us to think that Demise = Malladus. It's probably just one of the many things about the different backstories in the series that don't quite match up, given its "legend" nature and development process.