Here is the full list of all 31 Achtung! Cthulhu Tactics achievements.
Kill an enemy dealing 10 points more than their current HP
Hit 3 enemies in a single explosion
Kill an enemy due to the bonus critical hit damage
Complete a mission with at least 1 character not dealing any damage
Completed the whole Tutorial mission (with Tutorial active)
Complete a side mission
1 player Character kills 3 more enemies in a single turn
Have 3 characters Incapacitated and pick one up with Stay With Me
Have 3 characters damage a single target without killing it
A character is missed by 5 attacks in the same turn
Kill an unrevealed enemy
A character is hit by 5 attacks in the same turn without being rendered unconscious
Have characters use 3 limited use items in a turn
Take a gun from full mag to empty in a single turn
Have 1 character use 6 Momentum in a single turn
Kill a Shoggoth section entirely surrounded by other Shoggoth sections
All allies suffered from a Psychological Effect this turn
All allies are staggered at the same time
Do all missions in a single campaign
Complete all main and side objectives in main missions
Complete a mission without taking any damage
Complete the campaign
Complete a mission with all characters having been rendered Incapacitated at least once
Kill 100 enemies overall
Kill 200 enemies overall
Throw 20 grenades
Take each item on a mission
Take each mod on a mission
Use 10 medkits
Collected all other achievements
Completed the game on Mythic difficulty