Visible crew/equipment: During the warehouse battle, around when the Doctor tells Donna, "Hold on, I'm coming", the film crew can be seen reflected in a door at the right of screen. (00:28:20)
Continuity mistake: When Colonel Mace confronts Commander Skorr, he raises his gun twice; once in one shot, and immediately after in the other. (00:30:30)
Continuity mistake: Near the end, when Luke teleports and switches places with the Doctor on the Sontaran ship, Luke catches the atmospheric converter's switch twice, once in the wide shot and then again in his POV. (00:40:25)
Continuity mistake: When the Doctor activates the teleport, Donna is onboard the Sontaran ship, holding a cell phone in her left hand. When she arrives in the basement of the ATMOS factory, she's holding the rubber mallet in her left hand, and her right hand is empty, with the phone nowhere to be seen. (00:32:40)
Continuity mistake: When the Doctor pulls out a TARDIS key to give to Donna, the exact position of the key in his hand changes between shots. (00:05:00)
Other mistake: Just before the Doctor ignites the atmosphere, Sylvia's house is getting dangerously full of gas. When Sylvia and Wilf go outside after the air is cleared, the inside of their house is completely clear. Meanwhile, back at the Rattigan Academy, there is still gas lingering in the air. (00:34:43 - 00:37:15)
Factual error: The Doctor sets the atmosphere on fire, but only the upper part burns. The atmosphere extends from the Earth's surface (where it is densest) upwards, and so the flames would come right down to the ground, burning everyone to death. Of course that wouldn't work with the plot, so artistic licence has been applied.
Factual error: Colonel Mace says the Sontaran ship is orbiting 5,000 miles (8,050 km) above the Earth. However, in shots of and from the ship in both this episode and "The Sontaran Stratagem", the Earth appears far too small for the ship to be that close, with the ship's true distance appearing to be well over double that. (00:08:34)
Continuity mistake: When Donna is sneaking around the Sontaran ship, she's carrying Martha's old phone, which she's using to stay in touch with the Doctor, and the rubber mallet from the TARDIS. There are times when one of the two objects, the phone more often, is missing from her hands with no explanation.
Other mistake: When the Earth's nuclear launch sites are being brought online, country by country, in preparation for a strike at the Sontaran ship, Russia is puzzlingly omitted, even though North Korea of all nations is included. (00:17:20)
Chosen answer: No, no information is avalible for the identity of the entity.
Repo_Man