Here is the full list of all 18 TINY METAL: FULL METAL RUMBLE achievements.
Buy 10,000 worth of items
Own 19 Songs
Kill a Blits Mech with a Rifleman
Earn 600 after a campaign mission
Complete the “Safety First” challenge on Mision 1
Complete 5 Challenges
Heal a Blitz Mech to full health
Refuel a Archeon
Heal a Supply Plane to full health
Win a mission with exactly 7 units alive
Win with exactly 1 unit alive
Lose any mission on Easy
Win any mission on Easy
Score 150 or fewer points on a mission
Win any mission on Hard Difficulty
Win any mission on Master Difficulty
Complete 50 Challenges
Complete 99 Challenges