Here is the full list of all 30 Downward achievements.
Die from a Cactus.
Unlock all Meditation skills.
Obtain 2000 Skypieces.
Unlock all Wisdom skills.
Unlock all Endurance skills.
Survive your own recklessness.
Build four different rooms in the Merchant's Lair.
Obtain 1000 Skypieces.
Sell 15 items to the Merchant.
Unlock all Pursuance skills.
Unlock all Insight skills.
Obtain 500 Skypieces.
Obtain the Slingshot Artifact.
Buy all the upgrades of the Old Man's Room.
Reach the temple on top of the cliff.
Gather 50 Dry Artifacts.
Die from a Drone explosion.
Gather 25 Dry Artifacts.
Obtain the Double Jump Artifact.
Sell 5 items to the Merchant.
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-jumps.
Perform 500 wall-runs.
Perform 500 double jumps.
Perform 500 slingshots.