Which 'Doctor Who' Monster is the Scariest?

Adipose


Notable appearance: Partners in Crime 
What are they? Eternally cheerful blobs of fat from Adipose 3
What makes them so scary? If you accidentally eat one of them, they'll absorb your extra fat — and then your not-so-extra bones, muscles and organs until there's nothing of you left. 
Do they want to murder you? Not intentionally.



Heavenly Host


Notable appearance: Voyage of the Damned
What are they? Service robots
What makes them so scary? They're impossibly strong and devoid of a moral compass. If ordered to kill, they'll get right to it, with the added creepy bonus of chanting, "Kill, kill, kill."
Do they want to murder you? They don't necessarily want to, but they will.



Clockwork Droid


Notable appearance: The Girl in the Fireplace
What are they? Androids
What makes them so scary? They get ideas — really, really bad ideas. After realizing their ship, the SS Madame de Pompadour, was in disrepair, they reasoned traveling back in time and returning with the real Madame de Pompadour's brain was the best course of action.
Do they want to murder you? Depends. Is there a spaceship named after you in the future?



Chula Nanogenes


Notable appearance: The Empty Child
What are they? Sub-atomic medical robots developed by the Chula
What makes them so scary? With limited intelligence, the nanogenes are prone to misunderstandings... Like when they thought all humans should have a gas mask permanently fused to their face. 
Do they want to murder you? No, but they might get confused and turn you into a zombie.



The Family of Blood


Notable appearance: Human Nature
What are they? Gaseous telepathic predators
What makes them so scary? They have to inhabit and control a host body (usually human) to survive. They also have a terrifying scarecrow army at their command. 
Do they want to murder you? Does possessing your body count?



The Midnight Monster


Notable appearance: Midnight
What is it? Unknown
What makes it so scary? The Doctor and his fellow passengers never found out what tore into their confined shuttle and possessed a woman named Sky. Fear of the unknown, an unknown that somehow mimicked speech after, during, and before others had even spoken, made this mysterious menace all the more terrifying. 
Does it want to murder you? Unknown. (Probably.)



Cybermen


Notable appearance: Rise of the Cybermen
What are they? Cybernetically augmented humanoids
What makes them so scary? They're super into "upgrading" humans, either replacing your body parts with robotic parts or transplanting your brain into a metal exoskeleton. 
Do they want to murder you? Not exactly. They just want to give you an upgrade!



The Beast


Notable appearance: The Satan Pit
What is he? A demon.
What makes him so scary? The sadistic monster thinks he's Satan and he can use his precognitive powers to terrorize and eventually kill his prey.
Does he want to murder you? You and everyone one else in the galaxy.



The Flood


Notable appearance: The Waters of Mars
What are they? Viral species from Mars
What makes them so scary? They can infect and "zombie-ify" humans with just a drop of water, and they really would like nothing better than to take over earth.
Do they want to murder you? As a means to an end, certainly.



Gangers


Notable appearance: The Rebel Flesh
What are they? Clones created from the Flesh (living programmable matter)
What makes them so scary? They aren't just physical clones. They possess all the memories and personalities of their original — plus a few handy flexibility/disjointed tricks. And sometimes they're not content to give up the life they remember, even if it's not one they lived. 
Do they want to murder you? Depends on the clone.



Daleks


Notable appearance: Parting of the Ways
What are they? Mutated descendants of the Kaleds of the planet Skaro
What makes them so scary? With a mantra like "Exterminate!", it's little wonder these space terrors are the Doctor's oldest adversary. They're consistently characterized by their intense hatred and disgust for all living things that aren't them. 
Do they want to murder you? Oh, most definitely.



Vashta Nerada 


Notable appearance: Silence in the Library
What are they? Microscopic carnivores
What makes them so scary? In a swarm, they're capable of stripping a human to the bone in mere milliseconds. And since they're sentient, they can then control the body and get it to walk around.
Do they want to murder you? Yup!



The Master


Notable appearance: The Sound of Drums
What is he? A Time Lord
What makes him so scary? He's the Doctor's equal in many ways, an orphan Time Lord of incredible intelligence, fortitude — and demented craziness. He looked into the Untempered Schism as a child, and he just hasn't been right since. 
Does he want to murder you? Eventually. He might want to torture you and your family first.



The Silence


Notable episode: Day of the Moon
What are they? A religious order
What  makes them so scary? They've been living on earth for years, influencing our advancements, but as soon as you look away from their face, you forget they were there. This makes them disturbingly hard to fight or catch.
Do they want to murder you? If you're in their way, count on it.



Weeping Angels


Notable episode: Blink
What are they? Quantum-locked humanoids 
What makes them so scary? While they can't move while being observed, as soon as your eyes are turned, the Weeping Angels are impossibly fast and deadly. And since they look like normal statues, you'll never notice until it's too late. 
Do they want to murder you? Not all the time. Sometimes they'll just drop you in a different time period — but don't count on that. They're fond of neck-snapping, too.



Which alien would you be the most terrified to encounter in a dark space alley? Let us know in the comments!