As stated earlier, there is a 1936 D Buffalo variety with 3 1/2 legs. Yours is a 1936 P (no D mint mark on the reverse under FIVE CENTS). Yours also has all four legs. A bit more research would have given you a better idea of what a missing leg Buff would look like. Yours is also environmentally damaged. Perhaps you have mistaken the rust/crud on the reverse for a worn mint mark? HOWEVER...you found a Buffalo Nickel! Some of us would be extremely happy (myself included) to find something so old for nothing/face value. Congratulations!