The Chimera is part of the Bruen Ops weapon platform in Modern Warfare 2. The Chimera is said to be a stealth weapon that can be used at short to medium ranges. It has a built-in suppressor that makes it quiet. You can do a free challenge to unlock multiplayer, Warzone 2, and DMZ, or you can buy a bundle from the store.
Warzone Battle Royale unlock challenge
Challenge: Use an assault rifle to kill two operators in 15 different games.
This is pretty easy to understand. Just pick up an assault rifle from the ground, get one from a loadout drop, or buy your own custom primary assault rifle loadout from a Buy Station. The way this is written means that AI opponents in Strongholds and Black Sites won't count, so make sure you get rid of at least two human players during your match.
DMZ unlock challenge
Challenge: Get the weapon out of the new Building 21 in the DMZ.
This is a new secret building, and players will have to find it and figure out how to get into the area. We'll add to this guide when we know everything you need to know to get the weapon through DMZ exfil.
Modern Warfare 2 unlock challenge
Challenge: Use an assault rifle to kill two operators in 15 different games.
This is pretty easy to understand. Grab your favorite assault rifle and you're ready to play. The way this is written means that AI opponents won't count in Invasion, so make sure you get rid of at least two human players during your match.
Store bundle
You can also buy a weapon blueprint for the Chimera as part of a set of cosmetics. The Dark Skies bundle costs $12 and includes the blueprint for the Chimera Darkcell weapon and three small cosmetic items.
Buy it here
We can also unlock it for you by doing the challenge in MW 2 or Warzone for you.
Buy the Chimera unlock here.
The easiest way to finish the challenge is probably through multiplayer, but if you don't have Modern Warfare 2, it shouldn't be too hard to finish the challenge in Warzone 2.