I can't see any difference in the shape, just the discolouration, which looks to be typical for these cupro-nickel coins, particularly if they have spent time in a harsh environment. Surprisingly alkali - particularly ammoniacal - seems to do more damage than acid. Coins dropped in farmyard manure turn this colour very quickly.
Just looks like a corroded/discoloured 20p to me? You can force them to do it by leaving them in a damp environment with bronze coins.
(There is an accelerated way of doing it with household items if you're really bored)
Quote: Surprisingly alkali - particularly ammoniacal - seems to do more damage than acid
Alkali solutions brown them over really quickly. Salt, white vinegar and aluminium foil in a bowl will 'copper tint' cupro-nickel coins pretty well if you get the balance right. I got bored and got the 'clean some coins' thing out of my system on 10p's one day during the recent slowdowns and noticed the reaction. Not totally relevant but you never know when you'll find yourself that bored.
Quote: the coin is real natural color no chemical or any thing like that
Not suggesting you've deliberately altered it, just pointing out that it can happen if kept under certain conditions.
The obverse/reverse photos are not really large or lit well enough to tell anything useful about it, and it doesn't look thin enough to be one of the '1p blank' strikes from the one large pic you uploaded.
It's been exposed to a harsh environment. I have seen several 20ps with similar discolouration. I am 99.9999% confident that this is not some sort of error. Not all coins that have been in the ground will be like Numisrob's example - the pH of the soil, the length of exposure and the treatment afterwards are all factors that will affect it. It does not look remotely like the colour of the 1p shown, at least to my eyes.