When a necklace is stained with blood during a spurned lover's suicide or a murder, a Misdreavus is born. The only corporeal component of these ghost-type pokemon is a blood-red necklace at its center, and while sleeping or hiding they sink back into the necklace as though it were a pokeball. Initially, a Misdreavus haunt, play vicious pranks on, or even kill the person who either killed them or who they blame for their death, but such a revenge does not allow their spirit to move on.
Instead, Misdreavus forget what they loved in life and become addicted to causing pain and terror in others. Their happiness seems entirely a thing of the past, and they only remember that they were happy when alive, not what it felt like to be happy. This fact creates a deep envy in them and causes them to torment others all the more, for the closest thing they feel to happiness or vitality is schadenfreude. Whether yanking people's hair, floating above them in their dreams, or making them lose their balance on staircases and steep hills with their haunting cry, they are a vicious pokemon which make even Haunter seem friendly, and for many people the sight of a Misdreavus is even scarier than their actual pranks.
It takes a skilled trainer to tame a Misdreavus, to put up with their haunting trickery long enough to to make them remember that there is more to life than suffering. But when they do, they are rewarded with a wonderful friend and a pokemon with the potential to achieve an amazing power.