This one’s more of a chronological headcanon - sequence of events and all.
After doing the three primary storylines on Zandalar, the Horde Champion was called home to Orgrimmar to go on a quest to recruit the Mag’har. After that was done, they returned to Zandalar to find dire news - the Blood Trolls had regrouped and were now launching a massive attack on Zuldazar’s northern border.
Cue the Zandalar Forever scenario. Blood trolls invade the city of Dazar’alor and destroy the Great Seal. Though Rastakhan slew Zul, the attack didn’t really end there. Mythrax still stood, and was getting ready to finish off the city…
When an Iron Star collided with his head.
Suddenly, Iron Skyreavers swarmed around the giant like wasps, hurling fireballs at him. Wolf Riders poured into the streets of the Zocalo and beat back the blood troll army, gronn-mounted artillery harrowing the retreating blood trolls. It was even too much for Mythrax to withstand, as he too retreated back to Nazmir, gravely wounded.
The Mag’har had arrived, and saved Dazar’alor.
Not only that, but they continued chasing the blood trolls all the way to Nazmir, and served as the tip of the spear as the Horde began laying siege to Uldir.