» Mon Sep 06, 2010 10:50 am
Keep in mind that the dragonborn weren't in lore before. Not that they or other parts of lore were retconned, but that this is an expanded piece for Skyrim that also attempts to explain some other interesting parts of history, such as what really made the bloodline of the Septims so special. The fact is that it is bound to create some inconsistencies, as previous lore was not built with the existence of dragonborn in mind, or that Thu-um was the language of dragons. Before Skyrim, the Septims were a sacred bloodline blessed by Akatosh, and Thu-um was an ancient Nordic art now used only by the Graybeards. When they decided to put the amulet on ol' Mankar, it wasn't with "Oh, he's a Dragonborn too" in mind. You can use this idea to explain it now, but the fact is that he wasn't wearing the Amulet because he was a dragonborn, as that idea just didn't exist when he did it.
The most likely scenario to me is that he had his own plane of Oblivion which allowed him to bend the rules. Mankar also did not utilize the same methods as Dagon to enter and exit Oblivion, which were the portals. Certainly you used an improvised portal to get there, but Mankar has his own ways of going there and back. Oblivion isn't always a "you're in there or you aren't" kind of deal. There are a few cases where one can simply walk into Oblivion without going through any sort of portal. Consider the Daedric shrine quest for Vaermina. You go into a simple fort to reclaim an item from a guy trapped in a coma. As you go deeper, things get strange, and suddenly you're standing in a black chasm with floating rocks connected by Daedric-style bridges. Oblivion can simply bleed into reality sometimes. The Infernal City also details how it's possible to have a bubble of Oblivion existing inside Mundus while still remaining a part of it's original dimension. In Paradise, Mankar governs reality to an extent (though apparently not completely due to his inability to be immortal in it). I believe it wasn't "his" plane of Oblivion per se, but a chunk of it leased from Dagon. I don't think it's possible for one to simply create their own plane of Oblivion, but he could have borrowed it and gained some level of control over it. With his own rules in effect and the fact that the amulet is no longer on Tamriel, he may have acquired the ability to wear it. In addition, this ability could extend to Lake Arrius Caverns if one assumes that the rules of Paradise have bled into that part of Tamriel (which would also make sense, given that it's the headquarters of the Mythic Dawn)
There is just one unexplained phenomenon, which is how his followers can have their souls transferred to Paradise when they die (which also extends to the Shivering Isles to some degree, see Big Head). The only answer I can think of is that they are Soultrapped to Paradise, and when they die their souls are literally contained in that plane of Oblivion.
But in the end, the fact remains that there is no official explanation for it. Because the nature of the dragonborn is invented now, and because Mankar's ability to wear the amulet is still unexplained, it can be simply shrugged off as "Oh, he's a dragonborn too". The only thing I can say for sure is that the dragonborn excuse was not used when they made it work like that. Who knows what they had in mind when they set that up.