I wear a huge dark cloak, not unlike the one of a wizard, I am the opposite of warm, I don't walk-I float, I prefer to be sad, not happy. I appear in clouds, not in the sky, I can only be extinguished by a happy spell, I will take your soul, if you cross my path. I am a foul creature, amongst the foulest, you might call me a light extinguisher. What am I?
A dementor from Harry Potter.