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