He obtains the combo card once he has reached level 40 or by defeating psychopath mechanic Jed Wright in Case 0.
It's a Mossberg shotgun with a pitchfork taped to it and it kills zombie by attaching the pitchfork and letting the shotgun rip!!!
Person 2: Did you get it from Case Zero?
Person 1: No, I gained it the hard way by levelling up to 40.