Here is the full list of all 30 Downward achievements.
Die from a Cactus.
Buy all the upgrades of the Old Man's Room.
Build four different rooms in the Merchant's Lair.
Unlock all Pursuance skills.
Unlock all Insight skills.
Unlock all Wisdom skills.
Unlock all Meditation skills.
Unlock all Endurance skills.
Obtain 2000 Skypieces.
Perform 500 wall-jumps.
Perform 500 double jumps.
Survive your own recklessness.
Obtain 1000 Skypieces.
Obtain 500 Skypieces.
Gather 50 Dry Artifacts.
Sell 15 items to the Merchant.
Obtain the Slingshot Artifact.
Gather 25 Dry Artifacts.
Die from a Drone explosion.
Reach the temple on top of the cliff.
Sell 5 items to the Merchant.
Obtain the Double Jump Artifact.
Exit the tutorial area.
Defeat your first golem.
Use the Mark for the first time.
Wake Up!
Get a Gold medal in the Challenges.
Get 10 Gold medals in the Challenges.
Perform 500 wall-runs.
Perform 500 slingshots.