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