The Black Hand Challenge is a quest in Of Orcs and Men.
When speaking to Spearhead at the Black Hand hideout, Arkail will have the option to challenge him to a duel. After Spearhead is defeated, he will tell Arkail to seek out Fox to challenge next.
Fox, however, will only agree to fight Arkail if he and Styx have already sought out Sarkyss. When Arkail beats Fox, she will tell him that his opponent is Monkey.
In order to challenge Monkey, Arkail has to clear out the goblins in shantytown for him. A successful duel results in Monkey telling Arkail that The Last is the final opponent he has to defeat.
The Last is uninterested in fighting Arkail until Arkail kills Dorek the Trainer. After Arkail defeats The Last, the "Hand shake" trophy will unlock.