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