These kind of things don't happen often. We have a new 'Mule' error discovery coin! Yup, not a discovery of an error coin but THE discovery coin! NGC Certifies First Known Sacagawea-Presidential Dollar Mule -https://www.ngccoin.com/news/article/8794/ngc-grades-sacagawea-presidential-mule-discovery-coin/ If it goes to auction I'm going to guess it'll sell for at least half a million dollars... but also, check your change! No really, it was found in someone's change and pretty recently! So theoretically we all have a chance of spotting the 2nd one of these It's a 2014-D Sacagawea on the obverse with a presidential dollar reverse (the statue of liberty design).