NGC 1978-S Jefferson nickel with strong clashed die obverse and no clashing on the reverse. Also, the coin has a minor rotated die reverse as well, with a 10 degree rotation.
Proof dies are very scarce with strong die clashes, since the dies are quickly repaired or retired when they develop die clashes.
Clashed dies occur when there is no planchet between the dies, resulting in the two dies clashing together and transferring some of their design to the opposing die.
PF69 Ultra Cameo with heavily frosted devices and mirrored fields.