Dark Ops challenges are secret challenges found in Black Ops 3. Dark Ops challenges are revealed as you earn them. They do not count towards percent complete.
Multiplayer

Relentless Killer
Earn 10 Relentless medals (20 kills without dying).
Unlocked: Calling Card

Brutal Killer
Earn a Brutal medal (25 kills without dying).
Unlocked: Calling Card

Nuclear Killer
Earn a Nuclear medal (30 kills without dying).
Unlocked: Calling Card

Frenzy Killer
Earn a Frenzy kill medal (5 rapid kills).
Unlocked: Calling Card

Super Killer
Earn a Super Kill medal (6 rapid kills).
Unlocked: Calling Card

Mega Killer
Earn a Mega Kill medal (7 rapid kills).
Unlocked: Calling Card

Ultra Killer
Earn a Ultra Kill medal (8 rapid kills).
Unlocked: Calling Card

Chain Killer
Earn a Kill Chain medal (9 or more rapid kills).
Unlocked: Calling Card

Nuked Out
Earn a Nuclear medal in FFA without using scorestreak rewards.
Unlocked: Calling Card

Obtained
Earn Dark Matter by earning Diamond Camo on all weapons in the game.
Unlocked: Calling Card

Trick Shot
Destroy an HC-XD with a Combat Axe.
Unlocked: Calling Card

Dr. Lung
Kill an enemy underwater when you are both close to drowning.
Unlocked: Calling Card

Calamity
Kill an entire enemy team of 6 or more players in a very short time with a Specialist weapon.
Unlocked: Calling Card

Finish the Job
Kill an enemy who survived damage from 5 teammates in the same life.
Unlocked: Calling Card

100 Percenter
Complete 100% of all multiplayer challenges.
Unlocked: Calling Card
Zombies

Apocalypse Averted
In Shadows of Evil, help the others.
Unlocked: Calling Card

Prestigious Protagonist
Enter Prestige Mode after completing Deresurrectionist (Level 35)
Unlocked: Calling Card

Home Sweet Home
In Revelations, fix the universe.
Unlocked: Calling Card

Primis Rulz
Complete all the zombie story quests.
Unlocked: Calling Card