Curse of the Pharaohs III
After completing Blood in the Water, the final leg of the Curse of the Pharaohs quest becomes available. You should definitely knock off the Motherless Child side quest before leaving the necropolis, but after that, head back to the Temple of Karnak to confront Isidora. Scans will show jackalmen are now guarding the temple.
You can bypass most of them by proceeding over the rooftops to Isidora's location.
Use Senu to tag the hostiles inside, then enter the hall through the high windows. For a stealth kill, position yourself by Isidora, then drop kill a patroller while no one else is looking. You can then chain kill or sneak kill the priestess herself.
If you do get spotted, Isidora will run, and everyone else will attack. Withdraw to the overhead balcony and snipe, or run to the front door and use it as choke point to take out pursuers. No matter how you take out Isidora, confirming the kill shows that you've been fooled by an illusion.
Proceed to Isidora's quarters. There is a tiny force of soldier at the end of the walkway that can be easily sniped from a distance.
At the base of the statue, turn left and follow your marker to Isidora's door. It's locked, but look up and right for an open window.
Search the room for clues. One is behind a loose stone in the wall, which you will have to 'carry' away before you can access it.
These clues lead you to the Tomb of Tuntankhamun.
A long cutscene ends with you squaring off against the spectral boyking himself.
Tut's attacks are powerful and slow. His combo attacks also grow longer as his health decrease- you may have to dodge three or four swings before you can counterattack. A great weapon here is Tut's own dagger set, which you can secure during the National Treasures quest, though many other dual blades will work as well. Unlike some other pharoahs, Tut does seem to be disrupted by taking large amount of damage during an attack, and dual blades certainly give you the means.
When Tut dies, you'll get his spear, and a glowing ball of light (much like the one in Love or Duty) will guide you back to the world of the living.
You will doubtless encounter hostiles during your scramble, but none with enough mojo to kill you before you dash out of range.
After an extended cutscene, the mission completes.
The bit about mercy is nice, everyone could do with a bit more of that, but Bayek's decision to give the orb to Sutekh is frankly appalling. Even if Sutekh could be trusted to defend the orb's secret with his life (which seems unlikely), he has no resources- no money, no tools, no network of agents. He can barely stand up. And anyone looking for the orb will probably make a point of tracking down Ramsses' descendant's anyway- it certainly didn't seem to present a problem for Isidora. Still, he's gone when Bayek returns to the Valley, and Layla isn't hip-deep in walking Pharaohs, so one supposes it must have worked out in the end.