​Wake the Sleeper Agent in Blackout is one of the most cryptic challenges in Call of Duty: Black Ops 4's battle royale mode. It was even near impossible at a point because it required players to play as Reznov, a character unattainable at the time. Way to go there, Treyarch. 

The Stained White T-Shirt item once completed rewards Black Ops fan-favorite protagonist Mason as a playable character in Blackout. 

Here's how to complete the challenges.

Outside of the initial step, the rest is very straightforward. The two most difficult parts are actually obtaining the item and then the first step: Wake the Sleeper Agent. 

The Stained White T-Shirt is only found in crates so there's a little RNG involved there. Once you've obtained the shirt though, head to Array because that's where you awaken Mason. 

Wake the Sleeper Agent in Blackout: How to Unlock Mason

Once you've arrived in Array, head to the big radio tower in the middle of the POI and hit the button on the terminal. It's the same button that plays the emergency radio. Finally, once you've completed the first two steps, just stay alive. That's it. 

If you attempt this challenge in solos, you must stay alive until top 15. Duos is top eight and squads is top four. You must have the t-shirt in your inventory too so don't go ahead dropping it after awaking the sleeper agent.

There you have it! You have unlocked Mason, one of the most elusive characters in Blackout. 

Photo courtesy of Activision