Black Ops 2: The Master Killer Calling Card (Chain Kill, Nuclear Killer Challenges)
Finally getting the master killer title in Black Ops 2. Requires you to complete all Killer challenges in Black Ops 2, which include:
Bloodthirsty Killer III (30 5-kill gunstreaks)
Merciless Killer III (15 10-kill gunstreaks)
Ruthless Killer III (5 15-kill gunstreaks)
Relentless Killer III (3 20-kill gunstreaks)
Brutal Killer (25 gunstreak)
Nuclear Killer (30 gunstreak)
Double Killer III (20 double kills)
Triple Killer III (20 triple kills)
Fury Killer (kill 4 players rapidly)
Frenzy Killer (5 rapid kills)
Super Killer (6 rapid kills)
Mega Killer (7 rapid kills)
Ultra Killer (8 rapid kills)
Chain Killer (9+ rapid kills)
Feed Greed III (10 quad feeds)
Just spray down scrubs in Chaos Mode with a LMG for yours. I mostly used a silenced LSAT with stock and quickdraw.
The song is called "The Scales of Struggle" by user/MrPokeahole.