Muriel

In season 2 we hear about the book of life and how it can erase anyone (human or not) from reality as if they never existed. (I wonder what other things it could do... Any ideas?)

But we never actually see it and it's all kind of... dismissed

Maybe it'll come back in season 3 idk but anyway, the question is:

What would happen if the book of life does get used in some way?

So I saw on some Tumblr post that Muriel had a different name at some point, and so did Crowley and Aziraphale, but i haven't been able to find anything on it.

Would someone be able to look at stuff and reply to me please?

Thanks!!

(P.S. it's kind of really important for a head-canon i have)