The 1937-D 3 legged buffalo was made from a broken dye printer at the Denver mint.
Many where released into general population before inspectors caught the problem.
There are fakes were they try to sand down the one leg, so here are a few things to look for.
1.The farthest back leg will have less then normal.
2.There are dots on the belly that seem out of place.
3.The "P" and "U" from the Pluribus and Unum will be further back then the normal buffalo.
If you have all these find a specialist and get it cheeked
A mint condition one could be worth $20,000 plus.
A not so good one goes for about $1,000.