Doctor Who: EVERY NuWho Villain And Monster Ranked Worst To Best

Appear in: Flatline.

Back in 2017, the British Board of Film Classification (BBFC) officially rated Peter Capaldi's Twelfth Doctor era as the darkest of NuWho, with an appropriately numbered twelve 12-rated episodes. Although Series 8's Flatline was classified PG, the episode certainly highlighted the darker tone of Capaldi's run.

The Boneless were hostile two-dimensional invaders who eventually converted into three dimensions by using their victims as avatars to move about. However, they're far more terrifying in 2D: slithering around like rivulets on the walls and ceilings and sucking people up from the floor. There's also more a palpable sense of jeopardy when Clara and Rigsy narrowly escape the Boneless than when they're being chased by the glitchy 3D manifestations; however there is one scene in the tunnels where they resemble the frightening shadow demons from the film Ghost.

Add their ability to leech dimension energy from the TARDIS causing the exterior to shrink, restore flatten objects into 3D, and emit some scary screams and creepy chirruping, the Boneless are one of the best one-time villains.