I think the manga referanced him 'leaving this world' but then, thats non canon anyhow.
I think his intentions are more confusing than probably even his origins. He seems like a genuine chap at first, like guiding Link in his quest to save Termina. But then, does he truly care about Termina? Maybe he just wanted the mask before the moon fell, and didn't care about what happens so long as her departs with the mask in toe.
Though he also seemed abit gutted that the power had left the mask at the end, though not surprised. So I wonder if he wanted the mask with it's power? But again, he seemed not to angry at it, gave some farewell words, and departed to what I belive to be Hyrule by the way he said 'You should be getting back soon aswell' so it makes you wonder, is he really so mysterious?
Making him nothing more than an eccentric mask collector (with Bipolar?) who had heard stories of this one wonderfully evil mask, and he just had to have it. He probably would have known how to keep the mask under wraps aswell, but the mask called out to the Skull Kid in a effort to preserve itself. I'm sure if the HMS wanted to use it for bad intentions the mask would have sensed it and not lured the Skull Kid.
But though this makes sense to me, I dunno if I believe it.
Maybe he is a very late descendant of the Ancient ones, and through his life searching for his ancestors relic he grew ever so fond of masks? But Majora's Mask was his life goal? I dunno, I could genuinely just type and type about this, but it's nothing more than random ideas that I'm sure have no merit ^^. So I shall stop there
