Here is the full list of all 16 Nightmare of Decay achievements.
Finish the campaign on any difficulty.
Kill the Monstrous Beast in the campaign.
Complete the favor for the creature in the hole.
Kill the Meat Golem in the campaign.
Finish the campaign on hard difficulty.
Finish the campaign on any difficulty in under 1 hour.
Successfully escape from the dungeon in Dungeon Escape mode.
Survive past wave 10 in Horde Mode.
Finish the campaign on any difficulty using only the Survival Knife.
Finish the campaign on any difficulty using only melee weapons.
Finish the campaign on any difficulty without sprinting.
Finish Randomizer mode on any difficulty.
Finish Randomizer mode on hard difficulty.
Finish the campaign on any difficulty without saving or loading.
Finish the campaign on hard difficulty without saving or loading.
Finish the campaign on any difficulty without using any healing items.