Mercy is a telepath, Magician. She is the daughter of Merlin Michael and Mission Michael. She is the second of Steve Sharp's Wives. Steve, Sue, Dewey and Sheila meet her on their adventure to San Francisco which they took aboard Dewey's Sailboat, Executive Suite. Mercy loved sailing, and Steve has named two sailboats after her: Have Mercy and Mercy Mercy.
Her family owns the restaurant and magic theatre named Merlin's.
Mercy's full name is Mercy Michael Sharp, after an unofficial marriage to Steve; and she had four children with Steve: see Steve's Wives and Children. Michael is her maiden name: she says (of her son) "Michael Steven Sharp. That's after Merlin Michael the great Magician". Then, Steve asks for his "wives" to keep their full existing names and add "Sharp" as the last name, see Steve's Name Conversation. From their reactions, it's apparent they follow up with it.