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