Here is the full list of all 31 Achtung! Cthulhu Tactics achievements.
Kill an enemy dealing 10 points more than their current HP
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)
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
Hit 3 enemies in a single explosion
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
Complete a side mission
Completed the game on Mythic difficulty