1978 Fiji 20c mule
Among the many different mules struck at the Royal Australian Mint in the 1970s is the 1978 Australian 20c struck with a Fijian 20c reverse. There is no question that these coins were struck at the Royal Australian Mint, as it was responsible for striking both Australian and Fijian 20c pieces in 1978, but beyond that, details are scarce.
At least two examples are known with both known examples apparently exhibiting similar hairline scratches (Eigner, https://www.drakesterling.com/australia-1978-twenty-cent-fiji-mule-pcgs-ms62-47341245). It is unclear when they were first publicised but Jon Saxton's example appeared to have been on his website since at least December 2004 (Saxton, http://www.triton.vg/errors.html).
The Jon Saxton specimen was sold by Noble Numismatics' March 2015 sale for $21,960.