Here is the full list of all 18 Outbreak: The New Nightmare achievements.
Defeated your first undead threat.
Defeated 100 undead threats.
Defeated 1000 undead threats.
Healed yourself 20 times.
Cleared your first scenario!
Cleared 10 scenarios.
Healed yourself.
Cleared the Tutorial scenario.
Cleared the Outbreak scenario.
Successfully overcame a puzzle.
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.