Click multiplayer to view the map
Locate and
on duel and brawl
Use left and right bumpers to tab to 1 v 1 Duel (Player vs Player)
Win 20 Duels to unlock
I would suggest going through the basic and advanced tutorials before trying for this achievement. Going through a story mode will also help you become accustomed to the timing of blocks and parries. My strategy is to let the other player swing until they are out of stamina then deliver heavy blows. Timing with parries is tough but effective. When I first started, I used the 1st Viking (Raider) as he can pick up, run, and through people off cliffs with a double tap of