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