6. Cubone
What is it: Cubone is classed as the Lonely Pokémon, and is a Ground type from Kanto, where the original Pokémon games are based. It has a great ability for double battles, LightningRod, which draws all Electric type moves to it. The thing is, Electric moves won't hit Ground types, so it basically nullifies the move.
Why is it creepy: Well, the skull it wears on its head is actually the skull of its dead mother. No-one knows what its actual face looks like, as even Pokémon eggs of Cubone are born with the skull already on (I do not even know how that works). It also sees a likeness of its mother in the moon, so cries at the full moon staining the skull. It also makes a hollow rattle when it cries alerting Pokémon trainers to its presence. So remember when you catch one at night, and shove it into a ball, it was crying about its dead mother whilst wearing her bones.