Ballad of... was played once on the American edition of Whose Line.
Ballad of is a specific version of Duet. The two singers sing to an audience member as a western ballad. It was only tried once, but it worked well. The result was that Wayne Brady and Brad Sherwood sang "The Ballad of Leonard The Lawyer", which sounded as though it was inspired by Johnny Cash - particularly on Brad's account. The song featured the chorus "He'll lock you up faster than fssshhht", which Brad attempted to sing at the same time as Wayne but with no success.