Here is the full list of all 21 The Aquatic Adventure of the Last Human achievements.
Defeated The Worm
You died.
Defeated The Fathers
Defeated The Tranquil
Defeated The False Light
Defeated The Chain Gang
Defeated The Defiler
Defeated The Forgotten One
Defeated The Parasite
Defeated The Experiment
Defeated The Heart of the City
Defeated The Guardian
Complete the game
Find all upgrades
Read all Holotapes
kill 100 fish
Incapacitate the Tranquil
Complete the game without any upgrade crates
Unlock hardcore mode
Complete Hardcore mode
Complete Boss-rush Mode