Not an easy list to craft. One child's behind-the-sofa favorite is another's reason for rolling his eyes. But try, I will, based on those I find to be especially effective at ramping up the tension, creeping you out or just giving you nightmares. Feel free to submit your own if something else tripped your Fear Meter.
10. Mr. Sin (from The Talons of Weng-Chiang)Don't know about you, but I've always been a little edgy around killer puppets. Especially when they don't have facial expression. Though the Hinchcliffe-Holmes era was steeped in gothic horror, few of the monsters actually creeped me out. Hearing Mr. Sin, with his little pig brain, snort in pleasurable anticipation of a Ripper-like murder is one of the exceptions.
9. Early Cybermen (from Tomb of the Cybermen)
Before they were turned into space hoodlums, the Cybermen actually had a good turn as fearmongers. They were huge, faceless, had a hard-to-understand distorted voice, and were always accompanied by creepy music. "You will serve... uzzzzzz." And to make things even creepier, they died in an explosive and gory shaving cream emulsion. Gah!
8. New Who Daleks (from Dalek)
Face it, though the Daleks are the Doctor's number one foe, they've rarely been all that scary. Starting out rather effectively as literally tin-plated despots and Nazi stand-ins, they soon devolved into laughable pepperpots with screechy voices. When they made their comeback in the new Doctor Who, things had changed. The new bag of tricks retconned into the Daleks made a single Dalek able to effectively lay waste to the Earth, and both the writing and the performances sold it.
7. The Empty Child (from The Empty Child/The Doctor Dances)
Little Jamie gets infected by nanogenes that turn him into a little zombie able to infect others, giving THEM his childlike mind, wounds and gas-mask face. "Are you my mummy?" became the new creep-me-out of 2005. Children and puppets, eh? When Steven Moffat is good, he's very good.
6. Eldrad's hand (from The Hand of Fear)
The other Hinchcliffe-Holmes featured monster, Eldrad gets progressively less scary as he first turns into a woman, then a man. But as a disembodied hand, brrrr. I may be biased because this was my very first Doctor Who (and then my second, years later), but that creepy crawly hand was very effective. Tupperware and all.
5. Weeping Angels (from Blink)
Writer Steven Moffat scores another one with these statues that only come to life when you're not looking at them. Oh, the monsters aren't that scary to look at (indeed it's when you're NOT looking at them that they get dangerous), but the creepy feeling their premise generates gives them a place in this list. I actually know people who are creeped out by statues now.
4. Quill possessed by seaweed creature (Fury from the Deep)
Fury from the Deep hasn't survived to this day, but one of the few remaining clips is of Quill here silently screaming (actually, emitting a toxic gas) at the behest of the story's real monster. They keep running it in most clip collections and it SCARES THE BEJEEZUS OUT OF ME!
3. Autons (from Terror of the Autons)
The animated Auton mannequins are effective enough, but the ones in Terror take the cake. In this story, everything made of plastic could kill you. Inflatable mod chairs, plastic flowers, and this fellow here, and stumpy, ugly doll... that KILLS! This is pretty much the one that started morality cop Mary Whitehouse's campaign to cancel Doctor Who. Only took her 18 years.
2. The creature inside Sky (from Midnight)
A recent entry from Series 4, but I had to include it. We never see any "creature", but you won't believe how creepy someone repeating your words is. Then speaking at the same time you are. Then speaking ahead of you. Throw this thing in a truly claustrophobic episode and it becomes pure nightmare fuel.
1. The Beast (from The Impossible Planet/The Satan Pit)
"Don't turn around. If you do, you will die." If any Doctor Who monster ever came close to being the actual Devil, this is it. The monster's true appearance, that of a giant demon, is forgettable, but as a possessor of people, he wins my vote for most terrifying. A lot of it has to do with Gabriel Woolf's voice, who was great as Sutekh in Pyramids of Mars, but never this creepy. Plus: zombie hordes at his beck and call, access to all your deepest, darkest secrets, and instant tattooing!
Which DW monsters sent YOU scurrying behind the sofa?