Here is the full list of all 28 Stealthscape achievements.
Complete the first world
Complete the second world
Complete the third world
Complete the fourth world
Complete the fifth world
Complete the sixth world
Complete the seventh world
Complete the eighth world
Upload a custom stage to the Workshop
Subscribe to and play a custom stage from the Workshop
Fail a stage ten times in a row
Complete a stage
Fail a stage
Complete a stage without collecting any of the coins
Collect all the coins in a stage
Complete a stage without killing any of the enemies
Find all hidden Gold Coins in World A
Find all hidden Gold Coins in World B
Find all hidden Gold Coins in World C
Find all hidden Gold Coins in World D
Find all hidden Gold Coins in World E
Find all hidden Gold Coins in World F
Find all hidden Gold Coins in World G
Find all hidden Gold Coins in World H
Complete STLTHSCPE
Defeat the Corrupted Coin
Create at least 15 Stages
Defeat the Creator