One of the outfits that Bayek can wear in Assassin's Creed Origins is the Sekhmet Costume. It might not have any added benefit besides a cosmetic change for Bayek, but it is too cool to pass up. The cat-like helmet is what puts this costume a step above the rest and it is probably why most people are searching for it in the first place.
Fortunately, this is one legendary outfit that isn't too difficult to acquire seeing as all you have to do is complete a side quest. It is recommended that you reach level eight before attempting this, and completing the quest will also reward you with 800 XP.
Head To Yamu In Lake Mareotis
Completed a quest called Ulterior Votive will unlock a new side quest in a place called Yamu in the region of Lake Mareotis. It is located on the water and, once it is completed, you will be asked to speak to a man named Menehet, which is the start of a side quest called Lady of Slaughter.
Find A Man Named Menehet To Start The 'Lady Of Slaughter' Side Quest
Menehet, a priest, can be found at the Temple of Sekhmet in Yamu on the south side of the city, one of the best areas in the game. A cutscene will play that explains how his champion for the fight has gone missing. Menehet needs to locate him before the High Priest finds out and holds the priest responsible for his absence.
Find Pamu
Menehet will let you know that the fighter's name is Pamu and that his home is near the market, but the tavern is a better place to look. Head there, as it will be marked on your map, and once in the area use Senu to locate the man. Unfortunately, he will be severely intoxicated and lying on the ground in the corner of the open-air tavern.
You will have to carry Pamu back to Menehet in the Temple of Sekhmet and Bayek will offer himself up in place of the drunkard for the fight.
Talk To The High Priest
Menehet will tell you to speak to the High Priest in the temple courtyard. You will tell him that you were sent to play the role of Sekhmet in the fight. Fortunately, he doesn't need to be convinced and will take your word for it that Pamu has fallen ill. The High Priest will ask you to follow him and he will place the legendary Sekhmet helmet atop your head.
Enter The Ring And Face Isfet
When you are ready to fight just enter the ring where a fighter armed with a spear will be awaiting your arrival. He will be playing the part of Isfet, the Evil One, and it is your job to defeat this enemy so the Goddess will show favor to Yamu.
Defeat Isfet
Defeating Isfet isn't all that difficult, which is why this storyline is not part of the main quest, but there are a few things you can do to make the battle easier. Using your heavy attack will cause Isfet to drop his shield, at which point you can then deal a series of light attacks to deplete his health.
You should also be aware that you won't be able to use your own weapon, rather, Bayek will be equipped with a spear called the Peasant's Scepter.
Be wary of Isfet's attacks as he will use his shield to hit you, as well as take jabs with his spear and perform spin moves with this weapon. These can be dodged, leaving Isfet's back open for an attack. You can also use your shield to block his attacks.
Many choose to use their Overpower Ability, which will knock Isfet off balance and leave him open for you to deal a lot of damage. You will be able to finish him off faster by using this ability during the fight.
Collect Your Rewards
Once Isfet is subdued, Bayek will bask in the glory of the cheers from the crowd. He will then enter a cutscene with Menehet. The latter will tell you how the High Priest came up with the story of the Goddess and Isfet, as well as how Bayek is always welcome in Yamu.
This will complete the quest, rewarding you with 800 XP, the Sekhmet Costume, and the Peasant's Scepter, which are decent rewards during the earlier stages of the game. While the outfit doesn't have any special qualities, it looks great on Bayek. The Peasant's Scepter is also a common weapon, so you can earn some Drachma by selling it to a blacksmith.