Here is the full list of all 18 Outbreak: The New Nightmare achievements.
Defeated 1000 undead threats.
Survived the first ten waves in Onslaught.
Solved 100 puzzles.
Cleared 10 scenarios.
Cleared the Shelter scenario.
Cleared the Cure scenario.
Cleared the Faith scenario.
Healed yourself 20 times.
You failed to survive.
Cleared a wave in Onslaught.
Cleared the Urban scenario.
Cleared the Outbreak scenario.
Defeated 100 undead threats.
Healed yourself.
Cleared your first scenario!
Cleared the Tutorial scenario.
Defeated your first undead threat.
Successfully overcame a puzzle.