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