Here is the full list of all 40 UnMetal achievements.
Finish the game.
Destroy General X's robo-tank without using electromagnetic grenades.
Destroy 5 drones by punching them.
Break all toilet doors.
Complete "Jerico's Heart".
Obtain Robert's photographs.
Destroy 9 mechanical spiders.
Put 20 guards to sleep.
Complete "A Thousand Eyes Are Watching You".
Reach level 8.
Complete "Boom Docks".
Obtain 5 potties.
Complete "Engineering Problems".
Defeat HUGEEL firing just 6 torpedoes.
Complete "The Barracks".
Reach level 6.
Complete "Welcome to the Jungle".
Complete "In the Lion's Den".
Reach level 4.
Complete "Something Stinks Really Bad".
Complete "The Great Escape".
Reach level 2.
Reach level 10.
Finish the game without using a potty.
Neutralize 5 guards using the slingshot.
Heal 20 guards.
Craft a Molotov cocktail.
Kill 5 Human-Piranha-hybrid things with the shredders.
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.
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.