Here is the full list of all 21 The Neon Boy achievements.
Complete Laboratory
Complete Valley
Complete Smeltery
Complete Techcenter
Complete Rift
Collect the first star
Collect all stars
Complete the level with the best time
Complete all levels with the best time
Die 1 Time
Die 10 Times
Die 100 Times
Die 1000 Times
Die 100 Times due to Liquid
Die 100 Times due to Saw
Die 100 Times due to Bullets
Die 100 Times due to Lazer
Die 100 Times due to Fire
Die 100 Times due to Mine
Die 100 Times due to Thorns
Complete the Game