How do you ask people to join your league and how do you ask people to duel?
1) Hit Select. Then type /invite, then type the name of the character you want to invite.
2) Once you meet, press left. Head to “nearby” and click on his name. A menu will come up. Click ‘Duel’ and that will invite the player to a duel. He has the right to turn you down, of course.