Copper Sentinel
From the MEGA Wiki
The Copper Sentinel is an outfit cosmetic for your Titan. It's unlocked by the Metropolis achievement: Complete 50 buildings across matches.
Equipping
In the lobby, pick a Titan and click Customize, then find the Copper Sentinel under Outfits and click Equip Item. Each Titan keeps its own look, so it has to be equipped per Titan. Until it's unlocked it can be previewed but not equipped.
Other outfits
Cosmetics
Unlocking
City Cap
Frontier Titan
Builder's Hard Hat
Iron Chef
Party Animal
Neighbourhood Beanie
High Society
Monarch
Titan Shades
Champion Shades