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