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