Powers: Black Bile and the ability to project it in powerful optic blasts much like oil in appearance
Shepard first approached Mystique in Cuba and tried to convince her to turn against Charles Xavier, that he and his could give her protection. Shepard gave her a necklace to contact him with and vanished. He continuously appeared and reappeared, always knowing where she was, stirring up trouble for Xavier’s newest agent. It was later revealed he was helping Shortpack to track down the murderer of Prudence Leighton, an arms dealer called Steinbeck and had insight into all Mystique's missions to some .
Shepard reported back to The Quiet Man (whom he referred to as “beloved”) and tried to manipulate Mystique at every turn, finally succeeding at one point. Shepard believed he’d totally duped Mystique and even bore witness to her murdering Fantomex and E.V.A on a beach apparently to protect their secret.
Shepard eventually saw Mystique as no longer useful when her cloaking device was turned off so he held Shortpack hostage having lured the little mutant to the Quiet Man’s lair. Mystique failed but somehow fled Genosha at supersonic speed. When Shepard tracked her down to New York he pulled a gun on her to finish the , believing she was disguised as Fantomex.
Actually Mystique had duped Shepard, and had communicated a plan to Fantomex on a sub-aural level that he could hear but others could not - by morphing her vocal cords. She and Fantomex grabbed Shepard and Fantomex revealed that Shepard was in fact Prudence's brother, who had joined hIS sister, who now inhabited the body of Steinbeck and had taken on the Quiet Man identity. Mystique chopped off Shepard's hand to get at his teleporter watch and went to deal with The Quiet Man.
The revelation of Prudence being the Quiet Man and being referred by Shepard as beloved hints a past incestuous relationship between the two.