Here is a Swedish 1 Krona from 1997. By mistake it was struck on a 5 Markka planchet. I know of only one more off-metal error like this from 1998.

The Swedish Mint in Eskilstuna imported planchets from the Mint in Finland and among them were a few 5 Markka planchets which almost have the same diameter but are made in another alloy which made the coins look a bit more yellow.

The weight of the 5 Markka planchet is 6.7 grams instead of 7.0 grams for the 1 Krona coin.

Here are the normal 1 Krona and
the normal 5 Markka from Finland:






Here is the off-metal error coin: