Mulliniks was most successful as a steady role player for the Blue Jays. Originally a shortstop with the Angels and Royals, he was the lefthanded component of a Blue Jay third-base platoon (with Garth Iorg) in the 1980s. When Mulliniks was injured during the home opener of the 1988 season, Kelly Gruber proved he was ready to become an everyday third baseman, and Mulliniks gracefully adapted to a reduced role as a lefthanded DH when he returned from the disabled list.
Not blessed with great defensive skills, Mulliniks nevertheless led AL third basemen in fielding percentage in three straight seasons, from 1984 to ’86. When he retired in 1992, he had set several Blue Jay club records at the plate, including the highest single-season batting average (.324 in 1984), most doubles by a lefthanded batter (34 in 1983), most seasons leading the club in pinch hits (three), most consecutive hits (eight), and most consecutive times on base (10). His father, Harvey, a former pitcher in the Yankee organization, proved a useful advisor to break Mulliniks out of batting slumps.