Doctor Who: 10 Easter Eggs, In-Jokes And References In The Magician's Apprentice
9. The Planet Karn
There is a distinctly Tom Baker feel to this story as not only is it a sort of sequel/prequel to Genesis it also features a return to a planet he first visited - Karn, the home of the mystical Sisterhood of Karn.
In The Brain Of Morbius, the Sisterhood are the keepers of the Eternal Flame which grants them near-immortality. After nearly forty years since their first appearance, the Sisterhood appeared again in the 50th anniversary short The Night Of The Doctor where they are responsible for aiding the Eighth Doctor's regeneration into the War Doctor. Here they protect the Twelfth Doctor from Voldemort and Nagini - sorry, Davros and Colony Sarff.
Karn and the Sisterhood can also be seen in the online prologue to this episode, which takes place during the story's opening few minutes.