Here is the full list of all 21 Silt achievements.
Without ever dying, find yourself and awaken the machine
Find and possess all of the other divers in a single playthrough
Awaken the Great Machine
Defeat the Gloom Flower
Possess every unique creature type
Defeat the Spider Crab
Kill 10 leeches in less than 5 seconds
Smash a machine
Electrocute another creature with an Electric Eel
Possess 8 unique creature types
Defeat the Kraken Tree
Shake off 10 leeches at once
Feed the birds
While possessing a poisoned creature, get eaten by another creature
Lead a shoal of at least 30 fish
Possess 5 unique creature types
Defeat the Gulper Eel
Head-butt another creature with the Blockhead
While possessing a creature, eat another creature
While possessing a creature, get eaten by another creature
Deal damage to the diver while possessing a creature