Counterfeit Or Legit 3-Legged Buffalo

I'm no expert...but to me the mint mark on the OPs coin looks like it is set farther left and tilted. Coops coins in straight and appears to start just off the E in One not under the E

Unless there was more that one die making these three leggers than I would say it is fake or altered.

There are some reasonably educational images of genuine and false 3 legged buffalos to be found on
Google Images.

Fake.

Could there? Possibly, but no other has ever turned up.

The problem with identifying a second one would be getting people to keep an open mind about the possibility. The knee jerk reaction is people take one look, compare it to the known one, see it doesn't match and just dismiss it out of hand. You see that a lot on the online forums. Someone comes in with a 1955, 72 or 69 S cents and ask "Is that a Doubeld die?" People take one look, see it isn't the major one for that year and say No, it should look like this." and post a picture of the "Big One" completely ignoring the fact that it MIGHT be one of the others known for that year.

Still the problem with this being a possible second die is that if a second die had received an extensive enough polishing to remove the front leg, I would expect it to have similar rear leg and distant E PLURIBUS UNUM to what the first die had.