Here is the full list of all 18 Zero Punctuation: Hatfall - there are Hatters Gonna Hat Edition achievements.
Get squashed 100 times by an item above during gameplay
Saved the world
Played all mini games at least once
Successfully calmed the wizard 50 times
Collected enough hats to bring about the end of the world
Collected 1000 Hats during normal gameplay
Encountered the Wizard 50 times
Affection meter hit maximum
The user elected to violate Hatchan immediately
The player has caught a hat without moving from their starting position
The user allowed all of the text in the Story Screen Minigame to pass before catching the hat
Collected 100 Hats during normal gameplay
The player has purchased and unlocked their first alter-ego from the Shop
Unlocked upon first play of any Hatfall mini game
Collected 10 Hats during normal gameplay
Collected 5000 Hats during normal gameplay
Get impaled by an item above 100 times during gameplay
The player has purchased and unlocked all alter-egos from the Shop