I think that the serpent thing from SIW 1 is actually kin to the Inter-Dimensional Being from TTLG.
I know they don't look alike, but the IDB shots in TTLG might have just been a hallucination, or something. Or the serpent could be a third-dimensional manifestation of the IDB's real form (shown in TTLG, when John was in the IDB's realm).
More info to come, maybe.