The US nickel was first issued in 1866. Please double-check your coin.
It depends on what you mean by mis-stamped. Please feel free to ask the question again an include more detail.
This is a novelty coin not made by the US mint and has no collectible value.
It's the usual practice of this site to answer a single question at a time. Please see:"What is the value of a 1940 US nickel?""What is the value of a 1942 US nickel?""What is the value of a 1944 US nickel?"
That is what is known as a war nickel, because nickel was needed for WWII, it was needed to change the composition of the nickel to one including 35% silver, as of the time of writing, your coin is worth $1.64 in silver content alone.
The US Mint did not issue an 1896 nickel with an "S" stamped on it. If you have one then it would seem as though someone stamped the coin sometime after it left the mint. Also please don't assume that because a coin is old it has to be made of silver. All US nickels except special "war nickels" made during 1942-45 are struck in the same alloy of 25% nickel and 75% copper.
As of 16 Feb 2018, the melt value of one US nickel is 4.4 cents.
This design is called either a buffalo nickel or an Indian head nickel; both names are about equally common. Please see the question "What is the value of a 1919 US nickel?" for more information.
A 1957 nickel is worth face value only, unless it's uncirculated or a proof coin.
In average condition, both coins are only worth their face value.