Shadows of the Scarab
These phylake-alikes patrols the north and south respectively, as you might expect from the name. You should really wait until you've gone up a few levels before facing them- even if you've gained level 40 more than a dozen times since completing the main game, the elastic nature of AC:O's level system means they'll still be a force to be reckoned with until your actual level number draws closer.
And even then they're no slouches- good at attack and defense, and will switch weapons to mimic and counter your own. Still, there's no dodging or countering a dual sword Chain Attack.
If you can, try to lead the Shadow off the road, and get his back to wall to prevent too much dodging. If you're having trouble with his counters, try keeping some distance and building adrenaline with warrior and light bow shots, then leaping in with special attacks once your meter fills. Keep up the pressure for the eventual win,then confirm your kill for a legendary weapon, and completion of the A Shadow Defeated objective.
This officially unlocks the Shadows of the Scarab sidequest.
Killing the other Shadow reveals a bounty notice with your face on it.
Follow your new marker out to the desert, where a skinned camel marks the start of your new trail.
Follow the blood and tracks to a battle-cum-execution site, complete with someone left buried in the sand to die.
Follow the tracks further to a rocky hideout.
There are some carbon crystals within, and many basic lootables, but the path forward is through a crack in the south wall.
Follow the trail up and out to the desert, and at last to a small shrine. Pick up the item on the altar.
This begins a fist-fight with Kawab, who is actually pretty good at this (and has aged in a way that say, Reda, has not).
He's quite quick, so you won't get anywhere by chasing after him. Best bets are to (1) wait for him to charge you, then beat him to the punch, (2) wait for him to leap at you, then pummel him as he gets to his feet, and (3) try to back him against the shrine so he can't dodge away.
When the fight is over, walk toward the story marker with Kawab.
Completing the final cutscene there completes the mission.
You can also sit with Kawab for a while here, if you choose.
You can catch up with him in the aftergame as well.