Rain Gods was a mini-episode made exclusively for the Doctor Who: The Complete Seventh Series DVD and Blu-ray box sets. It is adapted from the unused opening sequence of TV: The Doctor's Wife, which was previously also adapted as a comic strip. Unlike the comic, the mini-episode does not replace the aired opening of The Doctor's Wife.
Behind the scenes
While Steven Moffat is created as the writer on-screen, the story was actually written by Neil Gaiman (who was also erroneously credited as the writer of The Name of the Doctor on the DVD box)[1].