Here is the full list of all 18 Mundaun achievements.
Find Jeremias's key
Drive the Muvel
Fill the Muvel with hay
Finish the game without hurting an enemy
Finish the game without dying
Scare off the bees with smoke
Find the cave in the first area
Find the waterfall cave
Draw all the maps
Win the sleigh race
Drink all of the coffee
Show the Mountain Prisoner book to HR buried in the snow
Turn on the chair lift
Leave Mundaun as you came
Leave Mundaun changed
Don't leave Mundaun
Use one of the transport furniculars
Pick up rifle