Here is the full list of all 14 Mainframe Defenders achievements.
Finish the game on Easy difficulty
Finish a game with unit having 70+ hull or 15+ armor
Finish the game on Normal difficulty
Finish the game without any squad unit deaths
Complete the final mission
Unlock all units and items
Complete Matter Raid and pick up 5 caches
Kill a unit while this unit has 3 times the max heat
Kill a unit with 60+ Corrosion stacks
Apply 5 different status effects on a single enemy
Finish the game on Very Hard difficulty
Finish the game without using rare items
Finish the game while having 1000+ matter
Finish the game on Hard difficulty