Sketch cards are one-of-one, hand-drawn originals created by the licensed artist from a given set. Each one is a unique piece of art on a standard-size trading card, signed by the artist who created it.
These aren't printed — they're literally drawn by hand, which means no two are alike. Sketch cards sit at the intersection of art collecting and card collecting, and they appeal to collectors who value creativity and originality alongside the usual stats and signatures. If you pull one, you've got a genuine piece of original artwork in your collection.