1899 Belgium 50 Centimes
1899 Reverse Muled with a 1907 Obverse
NGC MS 63
This is a Belgium 50 Centimes struck during the reign of Leopold II. The reverse die is dated 1899 but was incorrectly muled with an obverse die dated 1907. Obviously this was an intentional muling to create a rarity and fantasy piece. In 1907, the mint used a die for the reverse dated 1899. This is not a restrike since the reverse die dated 1899 is not cancelled, corroded or rusted, but is as fresh as the obverse die from 1907.
This illustrated definition of a mule is from the glossary section of Mint Error News.
This should have been the correct obverse using the 1899 die, not the 1907 obverse die: