Here is the full list of all 21 Lab Chaos Playtest achievements.
Played the game for the first time
Mastered 2 levels
Mastered 10 levels
Mastered all World 1 levels
Beat World 1 Epic Challenge
Got a gold medal
Got 5 gold medals
Got 10 gold medals
Got 20 gold medals
Got all gold medals in World 1
Gained 25 stars
Gained 50 stars
Gained 100 stars
Gained all stars in World 1
Played 25 times
Played 50 times
Played 100 times
Played 500 times
Played 1000 times
Died by a sawblade hazard
Died by falling