The Stolen Earth
Colony Sarff visits the Maldovarium, a bar last seen in 2011's "A Good Man Goes to War". The scene features several returning aliens: the Sycorax, the Hath, the Ood and a Tivolian. The Shadow Proclamation, an intergalactic police force last appearing in 2008's "The Stolen Earth", also briefly returns, featuring the Shadow Architect (from the same episode) and a Judoon.