Mina asks you to do two things for her. Kill Dark Mages and hunt the undead. Do her this favor.

Monster to Hunt -
Magus of Dark Arts: Bone Snatcher, Bone Maker, Bone Collector, Bone Animator, Bone Slayer, Bone Sweeper, Bone Grinder, Bone Caster, Bone Puppeteer, Bone Scavenger, Bone Shaper, Skull Collector, Skull Animator,
Undead Monster: Trampled Men, Sacrificed Men, Behemoth Zombie, Requiem Lord, Requiem Priest, Requiem Behemoth

You've collected 200 ribs. Return to Mina to receive your reward. Continue collecting livers of undead if you like. After settling accounts for rib bones, you can start hunting Magus again.