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