1920 Copper Buffalo Nickel?

If it were on a cent planchet, then it would weight the same weight of a cent and be the same size as a cent in diameter. Then the devices would fall over the edge of the coin like this coin that was given to me by my brother in law.

In late 2015 a 1936 (?) Buff struck on a blank intended for a Nicaraguan centavo coin (bronze alloy) certified by PCGS sold for $7.5k, and other examples of off-metal strikes are known for Buffs.

That being said, a look the claimed composition of the one in the link provided for the supposed 1920 coin: according to that link the comp was determined by some unknown method to be 89/8/3 copper/zinc/tin, which would be a brass (tombac) 10% alloy with tin as the colorant and it would amenable to being struck into a coin; but I'm not sure how a blank of said material would have gotten into the press to be minted or if any coins of the era were minted of similar composition.

It just looks toned to me.

You may not have found it on the ground but someone else certainly did at some point since 1920. The dusty greenish brown color is entirely consistent with a cupronickel coin that has spent significant time in contact with soil- that is the color of corrosion.

I have found 2 Buffalo nickels in five years of metal detecting and they both looked like this one.They were so worn down I couldn't even make out the dates but they were about the same color as this one

A small test file mark on the edge will tell the story. If it is copper, the file mark would not affect the value.

There are a couple early date buffalos known on copper planchets, but the overwhelming likelyhood is that this is an environmentally discolored coin. Weight is not going to tell you anything because copper and nickel are almost exactly the same weight and density so any disk of the same size made of copper or nickel or any alloy of the two will all weigh the same to within tolerance ranges. For that reason a specific gravity test is also worthless. About the only non-destructive way to determine the composition will be XRF analysis. And even that has its shortcomings in that it only tests the surface (and very slightly below).