You may want to collect as much Crystal Relics which are randomly hidden in Chests you'll find througout the Game.
I was able to collect enough crystals during my second Playthrough.
For Vampire Knack you want to collect those ruby crystals.
Once you have enough (15), you may want to begin a Chapter select Game on easy. Switch your Character to Vampire Knack, finish one Chapter and this Trophy is yours.