It grants the power to stun and dominate a Graug, through a multi-stage QTE.
The whole process is detailed in the mission that unlocks the ability, Hunting Partners, by Torvin, creator of the method. Talion bleeds the back of the Graug's knee, the only un-armored portion of its body, then mounts a Caragor that has been attracted by the blood scent, to gain the extra speed equal to a Graug. Then, to lure it away while also stunning it in the head via Elf-shot. When it falls to the knee, then Talion must execute a multi-stage QTE as he climbs the Graug, until the Wraith finally dominates the beast's mind.