Bonus: Chupacabra
Many people, especially farmers, believe that Chupacabra are real. They are tiny creatures that suck the blood out of livestock, usually cows. Many people have reported seeing an unknown creature running around the farm around the same time that their livestock was mutilated.
Bonus: Sewer Alligator
Sewer gators are definitely myths, but it's easy to believe in NYC. There are stories of alligators roaming around in the sewers and that they are radioactive due to the nasty pollution.