In AC Mirage, you can have amazing-looking outfits that make Basim look the part of a legendary assassin, such as the Rostam’s Outfit. Referencing the ancient Persian hero, the outfit features black cloth with golden accents and armor pieces. To get this outfit, you’ll need to complete some tasks.
Here is how to get Rostam’s Outfit in Assassin’s Creed Mirage.
Getting Rostam’s Outfit in AC Mirage explained

You get Rostam’s Outfit by completing specific contracts. In this contract, known as ‘ The Marked Coins’, you must help merchants catch traitors. They have hired you to do this job, and there are marked coins as an identifier that will help you locate that suspect. After you catch him, you will be rewarded with Rostam’s outfit.
How to get Rostam’s Outfit upgrades
There are 2 schematic upgrades that you can get for the Rostam’s outfit. For that to happen, you first need to complete 2 additional contracts. With each completed contract, you will unlock a specific schematic. They are the following:
The Traitors Contract

You can accept this contract at the contract board in the hidden one’s bureau. Your target will be located around the Soap Boilers district near the Damascus Gate. You will be tasked with eliminating the target via environmental damage.
You can kill them without the environmental damage, but you will not get the bonus rewards if you do so. You must first sneak near the target and wait until he gets near areas that will do environmental damage, such as exploding vases or dropable objects. After you finish this, you will unlock the first schematic for Rostam’s Outfit upgrade in AC Mirage.
Orion’s Belt Contract

Same as before, you can accept this contract at the contract board in the hidden one’s bureau. Your target this time will be at the Qasir Saleh palace. You must reach there and then wait for the target to arrive. Once he does, you must now assassinate him via environmental damage.
As before, you stalk your target from the shadows and wait for the right moment to strike. As soon as the opportunity presents itself, go for it. After you finish this, you will unlock the second and final schematic for Rostam’s Outfit upgrade in AC Mirage.