 Although he occasionally plays keyboards and synthesiser in concerts, Mullen rarely sings during performances.He contributed backing vocals to the songs "Numb", "Get On Your Boots", "Moment of Surrender", "Elevation", "Miracle Drug", "Love and Peace or Else", "Unknown Caller", "Zoo Station" and "Daddy's Gonna Pay for Your Crashed Car" (only during Zoo TV Tour), and others.He occasionally performed a cover version of "Dirty Old Town" on the Zoo TV Tour.