Australian $2 struck on 10 euro cent planchet
Wrong planchet errors are fairly uncommon in modern times as both mints and security companies have equipment that should identify coins which do not meet specifications. In any case, a small number of Australian $2 coins were struck with 10 euro cent planchets, which is especially impressive given that the coins should weight 6.6g but the planchets weight just 4.1g. None of the known coins are struck well enough to show a year, but a number of pieces have reportedly been discovered since 2012 (Eigner, https://www.drakesterling.com/australia-two-dollar-struck-on-foreign-planchet-pcgs-au55-47101599).
The coins in question are a different alloy - Nordic gold rather than aluminium bronze - though they appear much the same as a regular Australian $2 coin, albeit very poorly struck. It is unknown how many examples are available, and while three examples may have once sold in a single auction (https://www.australian-coins.com/blog/2013/01/more-australian-two-dollar-error-coins-struck-on-euro-10c-planchets.html), they are rare coins.