Here is Pokémon Coin Fan’s theory:
The remaining possibility is that it is an error coin, and I think this possibility is the most likely.
The basis for this is that an error coin called “Zacian: Silver Rainbow Holofoil” was put up for sale on the Japanese auction site “Yahoo! Auction” around 2022.
Originally it was supposed to be a Silver Rainbow Holofoil, but it had the specifications of “Cinderace: Red Mirror Holofoil”, which was included in the first Pokemon coin collection.
From here on, this is just speculation, but the fact that “Nintendo/C/G/M” is engraved on the back makes it highly likely that it was produced between October 1996 and July 1998, and it is likely that the colour of the " Raichu Yellow Cracked Ice Holofoil C/G/M"from the same period was just used for the Lucky coin .
I’m guessing from this, but since “Nintendo/C/G/M” is engraved on the back, there is a high possibility that it was born between October 1996 and July 1998. I think the color of “Raichu: Yellow Cracked Ice Holofoil Nintendo/C/G/M” from the same period was used as it is for the Chansey coin.
Is this coin created by combining these two?
I think this is a good theory. Both silver Chansey deck coins and yellow Raichu deck coins were produced and distributed at the same time through similar means. Perhaps the Chansey coin was erroneously manufactured with the Raichu foil and made its way into a deck box where it was not identified as an oddity for all these years.