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