Here is the full list of all 26 Montero achievements.
Kill an enemy with a flint pistol shot
Kill the Goblin shaman
Completely clean the location from the devourers
Kill the Cultist
Kill the Phantasm
Kill the Unconquered
Kill the Skullbeast
Kill the Werewolf
Completely clean the location from the Witchseeds
Sharpen your weapon with sharpener & silica
Dig out the treasure chest
Use the chariot after completing the mission
Create an item on the workbench
Kill the enemy with a Shock skill
Reach 70 maximum health
Pick up the overripe Ungus from a safe distance
Defuse a trap
Kill the enemy with the Guillotine skill
Finish the fight with maximum hunger and stress
Finish the fight with maximum health
Finish the fight with 1 health
Eat something while you are fully fed
Completely explore the Merid location (the main monster should be alive)
Completely explore the Feamp location (the main monster should be alive)
Completely explore the Scold location (the main monster should be alive)
Maximize your inventory