Is there such thing as a six legged salamander?

Answer 1

No. However, some amphibians regenerate their legs very well, and if they're damaged in a certain way they can accidentally regenerate extra limbs. This is sometimes done to sell them for more money. Don't buy these animals, the way they're made is animal abuse.

Answer 2

yes there is read the monsterology hand book by Ernest Drake on page 10 under the unicorn

Answer 3

A lot of sirens from the family Sirenidae only have two legs, they only have forelegs.