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