The Duel in the Great Mound was a open confrontation between Black Panther and Erik Killmonger.
Erik Killmonger, now the king of Wakanda and supported by W'Kabi and his army, prepared shipments of Wakandan weapons to be distributed to operatives around the world, so they may spread it to other people of African descent so that they may fight back against their oppressors.
Overseeing the ships leaving Wakanda, he sees one of them shot down by T'Challa, making his return as Black Panther. Killmonger orders W'Kabi and his army against T'Challa, but he blasts them away with his kinetic energy.
Enraged at Killmonger's evil nature, Okoye and a few of her warriors got ready to attack Killmonger, who reveals he has taken one of the upgraded Habits for his own use.
During the fight, Nakia and Shuri join Okoye as they fight Killmonger. With M'Baku and the Jabari Tribe arriving to help the fight, T'Challa focuses his attention on Killmonger, who is about to hurt Shuri.