Agreed, a lot of things about Billy don't make sense.

@Strannger18 said:

He had vitals and corporal. It seems ghosts beforehand were the normal variety.

WHO is Billy?

I’m thinking they are referring to Billy Miles. See the S1 premier S7 finale and then S8 episodes Dead Live, Essence, and then Existence.

The Billy in this case is a murdered child who came back to his family as a ghost in the season 8 episode "Invocation".

Oh.

That was a very bizarre uncanny episode btw.