Here is the full list of all 11 Outbreak: Endless Nightmares achievements worth 1,000 gamerscore.
Enter the first anomaly.
Enter the second anomaly.
Enter the third anomaly.
Enter the fourth anomaly.
Enter the reckoning.
Complete the story.
Enter the tower of pain.
Reach limbo.
Return a conductor's coin to the conductor.
Repair a weapon with repair parts.
Upgrade a weapon with weapon parts.