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