Doctor Who: 9 Ways To Kill The Doctor Permanently

The Doctor Who universe is stuffed to the gills with weird aliens and mysterious organisations, so it won't come as too much of a surprise to learn that there's a planet out there whose people specialise in one thing, and one thing only: killing.

Series 10's Extremis kicks off with the Twelfth Doctor paying a visit to this unnamed planet, a location that we aren't given too much information about.

However, the main thing that we do learn is that the people of this world are extremely good at killing, and in fact, one of them states that they know how to execute "every living thing" in the galaxy - including Time Lords.

This is evidenced by the fact that Missy is about to be sentenced to death, and we're even told how the executioners intend to kill her. They'll use advanced technology to "stop both hearts, all three brain stems, and deliver a cellular shock wave" that permanently disables regenerations, and while Missy is eventually spared, if definitely seems like these executioners know what they're doing.

Destroying the hearts and brain stems of a Time Lord was even mentioned by Missy in The Magician's Apprentice: she states that this would "switch me off fast, before I can regenerate". Even earlier than this, River Song refuses to let the Doctor save the day in Forest Of The Dead, because it would burn out both his hearts, with no regeneration.

So yeah - aim for the hearts and the brain stem, and the Doctor is toast.