Alright! I have a theory that I'd like to share. ^^
Many people are concerned about, if the Earl is in fact Mana, how it would be possible since they were in the same place at the same time when Mana was called back as an akuma. It's still possible! (or maybe I'm just really crazy) When Allen called Mana back, he called back his soul into the akuma, which was then going to kill Allen to wear as a skin (sounds super creepy..). What if the Earl is only wearing Mana's skin, like an akuma? Because why couldn't the Earl do the same thing as akuma, which he creates?
In Hoshino's one shot, Continue, SPOILER KINDA the Earl takes over the main characters best friend. So who's to say that the Earl in D. Gray-Man can't do the same? So it's still possible that the Earl is Mana, or vica versa, just not the Mana that we know (technically). So the Earl is just using Manas body. I'm not sure how he could've gotten it if it was buried, but maybe he took it after Allen called Mana back. I'm sure if it is in fact what happened, Hoshino will have some kind of explanation. xD
A lot of people have stated why. Maybe because he thought it would make Neah want to join him again, cause he was talking about wanting to be by his side? Maybe he has crazy reasoning that, if he looked like Neah's brother, that would make the 14th more willing to join him again instead of try to kill him. Or maybe it was because it would make it harder for Neah/Allen to kill him? I thought it was interesting that neither the 14th nor Allen has seen the Earl in his human form yet. Cross did say that when Allen became the 14th, he would have to kill someone that he loved. Allen loves Mana more than anyone else! And the 14th wants to kill the Earl to become him. So it makes sense.
And that's just my two cents on it. :b
also, I've always imagined like, towards the end of a chapter where Allen encounters the Earl, he'd be in his human form and Allen would be like, "Mana...?" :gwah
And I've also wondered, why does Mana have golden eyes? It said so quite a few times in Lost Fragment of Snow... there can't be two more Noahs that no one knew about, right? That's been really bugging me.