Yeah, that feels a bit confusing now but I bet it will be revealed soon.
Like with the mirrors maybe he literally split himself in two, otherwise how could he be there with Allen.
Maybe the dog? Lmao or It was Mana the thing is.... it said in the storie Mana die on accident carriage while he and allen traveling around the world "when i say travel around the world it was the circus" maybe? Hehe.
So Allen wish for Mana to be alive that when "half the Millennium Earl" show up to revive Mana grave but turn into skeletal Akuma and cursed Allen that why he slash allen Eye to see the suffering of being akuma. You know allen had innocence arm that trigger to protect its master from Akuma So Mana Die Second time.
Mana is revealed to be one half of the Millennium Earl, who was "reincarnated" as the twins Mana and Nea D. Campbell.
I love all these reveals and flashbacks just I'm little confused now... Who cursed Allen in the beginning? He couldn't summon Mana as he isn't dead or did he?