Here is the full list of all 22 Hellmut: The Badass from Hell achievements.
Shoot 1,000 enemies with a single weapon.
Do 15.000 damage with barrels.
Kill at least three enemies with an exploding barrel.
Enter dungeons as the Orc Fairy.
Deal over 100,000 cumulative damage.
Complete Challenge mode in under 1 minute.
Shoot 10,000 shots.
Die for the first time.
Enter dungeons as the Rat King.
Complete Tutorial.
Unlock all Transformations.
Buy one of each item type in shop.
Kill one of every enemy type.
Stay in the shop for more than 20 minutes continuously.
Don't lose a single hitpoint in one level.
Complete one playthrough in under 20 minutes.
Defeat The Demon.
Acquire Professor Transformation.
Collect 5,000 Soulstones cumulative.
Use every weapon.
Kill The Demon at least 10 times after receiving Professor Transformation.
Play with all Transformations except the Professor.