Duck The Halls: A Robertson Family Christmas is the family’s certified platinum Christmas album and features performances with Luke Bryan, George Strait, and other country music icons.
Mallard’s “platinum album” clue was definitely intended to steer The Masked Singer viewers in the direction of a country singer, but Willie Robertson also has a platinum album.
As for the best-selling book mentioned in the clue package, Willie Robertson has a best-selling book he co-wrote with his wife (alongside writer Mark Schlabach) called The Duck Commander Family.