Heart & Soul - S4-E8
Continuity mistake: After Sam reads the newspaper article about Jim's death it cuts to him dropping in to see Melinda, and when he's looking at the framed photographs on the sideboard two of the closeups of the photos are flipped shots - the positions of the frames are reversed.
Answer: This "spirit" appears in several episodes throughout the rest of the season including the season finale. He's a "bad spirit" that is intent on keeping souls trapped on Earth. With the death of Andrea (her business partner) he wanted to make a deal with Melinda, to give him HER soul to release everyone else including Andrea to cross over.
Boobra