Ok, the foetus thing.
Voldemort made horcruxes throughout his evil reign. He chose to split his soul and put a piece of his soul into certain things. Ring, locket, diary, snake, diadem, and cup. He had split his soul so much, that when the killing curse rebounded off Harry and hit him, it split his soul once more, which attached itself to Harry.
So 6 intentional, 1 unintentional.
The piece of soul, when freed from the horcruxes, looks like that slimy foetus in the waiting room (place between heaven and hell?).
So when Harry was 'killed', it destroyed the last horcrux, rendering voldemort truly mortal and just a man, therefore killable.
Harry understood that he was a horcrux and was meant to die. So he didn't fight. He let himself die, to protect all of his friends etc.
He was able to come back due to Lily's protection, but he in turn protected all of his friends etc because he was willing to die for them. Hence why all voldemorts curses weren't binding and he kept missing them with his spells.
Then, it came down to just Harry and voldemort. And the elder wand would not turn on its true master.
So in the end, it was hallows, horcruxes, and Lily's protection all needed to destroy voldemort.
I am so sad.