Here is the full list of all 40 UnMetal achievements.
Reach level 2.
Complete "The Great Escape".
Complete "Something Stinks Really Bad".
Complete "In the Lion's Den".
Complete "Welcome to the Jungle".
Complete "The Barracks".
Complete "Engineering Problems".
Complete "Boom Docks".
Complete "A Thousand Eyes Are Watching You".
Complete "Jerico's Heart".
Finish the game.
Reach level 4.
Reach level 6.
Reach level 8.
Reach level 10.
Obtain Robert's photographs.
Finish the game without using a potty.
Neutralize 5 guards using the slingshot.
Heal 20 guards.
Put 20 guards to sleep.
Destroy 5 drones by punching them.
Destroy General X's robo-tank without using electromagnetic grenades.
Obtain 5 potties.
Craft a Molotov cocktail.
Kill 5 Human-Piranha-hybrid things with the shredders.
Destroy 9 mechanical spiders.
Die while tampering with items from your inventory.
Destroy 5 trucks in the barracks north parking lot before SPLASH MIKE does with his tank.
Complete the catacombs without destroying any cell gates.
Have 90 or more bullets at the same time.
Destroy 5 crates with the explosion of a single grenade.
Find 15 secrets in the game.
Defeat Sewerjunk without damaging it with the Flamethrower.
Defeat TAKUMA TAKAGASHI without letting him heal himself.
Break all toilet doors.
Defeat HUGEEL firing just 6 torpedoes.
Let SPLASH MIKE destroy all crates and trucks at the barracks.
Reach the ground floor in less than a minute when rushing to save the doctor.
Finish the game on hard difficulty.
Get the maximum experience possible in at least 5 chapters.