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