Yes, it's normal. It's one of the two new design for 2005 nickels. Soon you will be finding the other 2005 reverse design called "ocean in view". The motto E Pluribus Unum ("From many, one") has appeared on nickels since 1883 and on all circulating U.S. coins since around 1916, so this generally isn't a distinguishing characteristic. The most important characteristics are denomination, date, mintmark, and condition.
Current retail values for a 1937-D buffalo nickel with three legs range from $500 if very worn, up to about $1200 in AU condition. However you would need to have the coin examined in person because there are many counterfeits made by removing the leg from a normal nickel using jeweller's tools.
I believe from my research that the normal/regular state of nickel is a solid.
a normal buffalo can have 1 at a time
37.2 - 38.2 degree Celsius is the normal body temperature of a buffalo.
At standard temperature and pressure, nickel is solid.
The normal phase is solid.
Nickel chloride is a solid at normal temperatures.
Nickel Doesn't react with water under normal conditions
Same stuff as a normal-coloured buffalo would eat of course.
Your coin is over 70 years old so it's not surprising that the date is worn. And if you compare it to any other nickel in your pocket, you'll see that ALL US coins have their backs oriented 180º to the front, so your nickel is perfectly normal. Please see the Related Question for more information.
38.2 degree c