Dark and Ghost attacks do 1/2 damage.
Bug and Fighting do 2x.
Psychic does jack shit.
Everything else does whatever damage it's supposed to.
Can be found on Route 13 and in Great Chasm during the post game of Pokemon Black and Pokemon White, and on Route 120 in Pokemon Ruby, Sapphire, and Emerald. Learns Perish Song at Level 65.
Trainer 2: You lucky SOB! Can I borrow....
Trainer 1: Her.
Trainer 2: Her long enough to make an egg with my Ditto?
Trainer 1: Sure man, what are bros for?
Trainer 2: Awesome! Thanks man!