What's the scariest magical creature?
My first thought was of course to Dementors. They're creepy as hell! But then I was wondering whether they'd actually count as "creatures". I wonder whether perhaps they're too sentient or too life-like for me to be really calling them creatures. So I came up with something else.
I'm purely going on what I felt as a kid and this massive snake absolutely terrified me! I mean, it's a massive snake with really poisonous teeth and eyes that turn you to stone on a good day but kill you if you look at them directly!
So, what's your creepiest HP creature?