Here is the full list of all 22 Adventuring Gentleman achievements.
Defeated Goblin Gunner
Defeated King of the Mushrooms
First enemy killed
Defeated Artilerist
Defeated Battle Automoton
Defeated Goblin Wizard
Caught Flower Fairy
Defeated Diving Suit
Defeated Ornithopter
Defeated Steam Dragon
Freed Canterville Ghost
Defeated clockwork Sofia
Defeated Nutcracker King
Defeated mechanical Sofia
Fetched the Sun
Defeated mechanical God
Turned off Sired
Defeated Count in Yellow
Defeated King in Yellow
Defeated Many Eyed Moon
Looked at Dorian's Portrait
Defeated Selfish Giant