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Avenger: Kill an enemy that recently killed a teammate
Comeback: Kill an enemy after dying 3 or more times in a row
Efficiency: Kill multiple enemies with a single bullet
One Shot, One Kill: Kill an enemy at full health with a single shot from a Sniper
Savior: Kill an enemy before they kill a teammate
Bloodthirsty: 5 kills in a row without dying
Merciless: 10 kills in a row without dying
Ruthless: 15 kills in a row without dying
Relentless: 20 kills in a row without dying
Brutal: 25 kills in a row without dying
Nuclear: 30 kills in a row without dying
Denied: Kill an enemy while carrying the flag
Takedown: Kill a terrorist who's planting the bomb
Clutch: With no teammates alive, defuse the bomb when enemies are alive