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