The Bells of Saint John - S7-E8
Revealing mistake: During the sequence where Clara sets foot on the TARDIS for the first time, and she and the Doctor then stop the plane from crashing, there are some shots which make it fairly obvious that the mug of tea she's carrying is empty. (00:25:35)
Chosen answer: No, no information is avalible for the identity of the entity.
Repo_Man