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